The pre-dawn stampede at the massive Hindu festival in northern India created havoc. But order was restored swiftly in the next few hours.

On Wednesday morning, ambulances cut through a swarm of millions of people who had gathered in the city of Prayagraj. They ferried dozens of people to hospitals, some who had been trampled to death.

Local officials moved to resume the rites at the Maha Kumbh Mela, relying on thousands of “A.I.-powered” video cameras. Soon, the faithful were doing what they came for: bathing at the confluence of three rivers considered sacred, one of them mythical. A helicopter showered rose petals on seers leading the holy dip.

Officials had studied stampedes at earlier iterations of the festival. But as prepared and equipped as they seemed to be, they did not release even an initial death toll for nearly 15 hours after the tragedy.

What they kept releasing was good news: regular updates on how many people had completed the bathing ritual.

The dearth of information on the victims of the stampede, analysts said, appeared to be an official effort to cover up damage at an event that holds significance to the fortunes of political leaders. It left families of those searching for loved ones in the dark, running from hospital to morgue.

And it left a cloud over the official tally that was finally released on Wednesday evening — 30 dead and 90 injured.

Among those searching for their loved ones in the vacuum of information was Shiv Shankar Singh, 55, a retired army officer He and his wife had bathed at the confluence of the Ganges and Yamuna Rivers, and the mythical Sarasvati, soon after midnight, and then got caught in the stampede.

He searched for her all day, making his way on foot from hospital to hospital in an area where vehicular movement had been restricted for miles.

“Everybody was pushing everybody else. My wife fell down,” Mr. Singh said. “I grabbed a pole and stood on the ground. I saved myself, but I don’t know what happened to her.”

The Kumbh Mela, which happens every 12 years, is a massive undertaking by any standard. This year, because of a rare celestial alignment, it was deemed a once-in-a-century occurrence. The government in Uttar Pradesh, India’s most populous state, said it expected more than 400 million pilgrims and visitors to arrive in Prayagraj for the 45-day festival.

Yogi Adityanath, the state’s chief minister, is considered among the contenders to succeed Prime Minister Narendra Modi. Analysts said he put himself front and center as the organizer of the world’s largest gathering in an attempt to build his national profile as an administrator who could mix two things dear to India: faith and technology.

While assessing the preparations for the festival early in January, Mr. Adityanath, 52, had pointed fingers at his predecessors over the operation of past festivals, which had led to deadly stampedes. He said that he wanted arrangements that could be “a lesson to those who had made the organization of the Maha Kumbh synonymous with filth and stampede.”

“Yogi has been touted as larger-than-life, larger-than-Uttar Pradesh,” said Rasheed Kidwai, an author and political analyst. “The success of the event would have meant to announce to the world, ‘Here is a man who micromanaged a gathering of 400 million people effortlessly.’ This posturing would become important for the post-Modi era.”

The Uttar Pradesh government has a public relations budget of over $100 million for the year, and some of that goes to media outlets that provide friendly coverage.

It has also introduced a new social media policy that gives financial incentives to influencers who promote the state’s success, while promising action against the reporting of “government schemes in a wrong manner or with wrong intention,” according to news reports.

The hold of that influence was clear in the aftermath of the tragedy. Television channels headlined Mr. Adityanath’s regular phone conversations with Mr. Modi, 74, and that everything was under control. They repeated throughout the day a video statement by Mr. Adityanath, in which he made no mention of deaths but asked people to not fall for rumors.

But some saw through the public relations campaign.

“It is reminiscent of the opacity of Chief Minister Yogi Adityanath and his government after the widespread deaths during the second Covid-19 wave in March 2021, the scale of which was evident later when horrific images of bodies floating in the Ganga emerged,” The Hindu, a national newspaper, wrote in an editorial Thursday.

Mr. Adityanath has ordered a probe into the lapse. His officials have not explained what caused the delay in providing a casualty toll. His office did not respond to requests for comment.

Vikram Singh, a former police chief of Uttar Pradesh who has overseen arrangements in past Kumbhs, said a part of the delay could be attributed to the massive logistical demand of such a huge event. Officials would have been focused on evacuating the injured and getting them proper treatment, he said.

But he, too, struggled to understand the extent of the delay, which he said only fueled a rumor mill that “was working overtime” to put the death toll anywhere from 50 to 200 in the vacuum of official information.

The other Mr. Singh, who had been separated from his wife, went to the festival’s lost and found stands to look for her. He registered a complaint with her details. He went back to the confluence of the rivers. He walked from hospital to hospital and back to the festival site.

There, in the evening, Mr. Singh finally had good news at one of the lost and found centers. His wife had fallen down in the stampede but, luckily, wasn’t hurt and had been waiting for him for hours.

“If they had communicated, then I would have found her much earlier,” he said, referring to the lost and found booths. “But I am happy now that I found my wife.”

Pragati K.B. and Suhasini Raj contributed reporting from New Delhi.

Ahmed al-Shara, the leader of the rebel coalition that swept to power in Syria last month, has been declared the country’s interim president, a role that will see him navigate a time of untold change for a fractured nation.

Under Mr. al-Shara’s stewardship, Syria’s interim government will now face a delicate political transition after the overthrow of the dictatorship led by President Bashar al-Assad.

Among the many challenges he faces are uniting a complex patchwork of rebel groups, gaining control over multiple regions under the sway of powerful factions and rebuilding relations with the international community to undo crippling sanctions.

How did Mr. al-Shara rise to power?

Formerly known by his nom de guerre, Abu Mohammad al-Jolani, Mr. al-Shara spearheaded an offensive last month that ousted Mr. al-Assad and ended the Assad family’s iron grip on the country, which had lasted more than five decades.

Mr. al-Shara was the leader of Hayat Tahrir al-Sham, an Islamist rebel group once linked to Al Qaeda. His faction controlled most of Idlib Province, in northwestern Syria, during a long stalemate in the country’s civil war, which dragged on for nearly 14 years.

In late November, Mr. al-Shara launched the most significant challenge to Mr. al-Assad’s rule in a decade, capturing territory across several provinces without facing much resistance from the government’s military forces or from their powerful international allies Russia and Iran.

Hayat Tahrir al-Sham and other armed factions in the rebel coalition would be disbanded and integrated into the fledgling government’s armed forces, a spokesman for the coalition, Col. Hassan Abdel Ghani, announced on Wednesday. He also declared that the Constitution had been nullified and that the legislature and army formed under the Assad regime had been dissolved, according to the Syrian state news agency, SANA.

It was not immediately clear whether there was a broad consensus among armed groups across Syria about Mr. al-Shara’s appointment as interim president. It was also unclear how long the transitional period would last.

What is the new leader’s background?

Born in Saudi Arabia, Mr. al-Shara is the child of Syrian exiles, according to Arab media reports. In the late 1980s, his family moved back to Syria, and in 2003, he went to neighboring Iraq to join Al Qaeda and fight the American occupation. There, he spent several years in a U.S. prison, according to American officials.

Mr. al-Shara later emerged in Syria around the start of the civil war and formed the Nusra Front, an affiliate of Al Qaeda. He eventually broke ties with Al Qaeda, and the Nusra Front evolved into Hayat Tahrir al-Sham.

After sweeping to power in Syria last month, Mr. al-Shara has seemed to be trying to distance himself from his militant past, ditching his combat fatigues and donning a suit and tie as he welcomed a roster of foreign diplomats to Damascus, the Syrian capital. By eschewing global jihadist ambitions, Mr. al-Shara apparently hopes to gain international legitimacy, which would help to attract much-needed sanctions relief and funds for rebuilding.

There are signs that the strategy may be working.

Last month, the U.S. government — which has designated Hayat Tahrir al-Sham a terrorist organization — dropped a $10 million bounty on Mr. al-Shara’s head.

Washington has also eased some restrictions on humanitarian aid to Syria, and the European Union announced this week that it would lift some sanctions. Those moves should give Mr. al-Shara’s transitional government some breathing room as it attempts to build a more stable future.

What challenges does Syria face?

Mr. al-Shara has laid out lofty goals, including rebuilding state institutions, ridding the government of corruption and cronyism, and freeing the country from the torture and repression that came to define the Assad regime.

“What Syria needs today is greater than ever before,” he said in remarks published by SANA on Wednesday. “Just as we were determined to liberate it in the past, our duty now is to commit to rebuilding and advancing it.”

But many Syrians have questioned whether Mr. al-Shara can deliver on the ambitious promises and also reconcile his former rebel group’s militant Islamist roots with a largely secular state. Under the watchful eye of the international community, Mr. al-Shara has sought repeatedly to reassure minority communities, and he has pledged to build a country that is tolerant of other beliefs.

The new government has also vowed to hunt down and prosecute senior figures from the Assad years.

But accountability will be a daunting challenge, and there is mounting concern about revenge attacks on members of the old regime.

Adam Rasgon, Raja Abdulrahim, and Christina Goldbaum contributed reporting.

Salwan Momika, an Iraqi immigrant who set off enormous protests when he burned a Quran in Stockholm in 2023, has been killed, the Swedish Prosecution Authority said Thursday morning.

The police said that they had arrested five people and that a murder investigation had been launched. Mr. Momika had been set to appear in Stockholm District Court on Thursday on charges related to the 2023 incident, which resulted in protests in Sweden and across the Muslim world.

The Stockholm police, who declined to confirm that Mr. Momika had been killed, said that there had been a shooting late on Wednesday in Sodertalje, a city near Stockholm, and that a man had died. The prosecution authority then confirmed that Mr. Momika was that man.

Mr. Momika’s defense attorney, Anna Roth, said he had received death threats. The authorities did not say if they believed the killing was connected to Mr. Momika’s burning of the Quran.

Mr. Momika, a Christian, had set the Quran ablaze during Eid al-Adha, a major Islamic holiday, outside a mosque in Stockholm. He said that he was trying to raise awareness about the mistreatment and killing of Christian minorities by Islamists in some parts of the Muslim world.

“I am warning the Swedish people about the dangers of this book,” Mr. Momika had said through a megaphone outside the mosque.

The response from the Muslim world was swift and furious, with much of the criticism aimed at the Swedish authorities for not stopping the burning.

In Iraq, several hundred people stormed the Swedish Embassy in Baghdad and set parts of it ablaze. Iraq expelled Sweden’s ambassador and directed its ambassador to Sweden to withdraw from its embassy in Stockholm.

Egypt called the Quran burning “a disgraceful act.” And Morocco recalled its ambassador in Sweden, its state news agency reported.

The Swedish authorities had condemned Mr. Momika’s actions at the time, but the police granted a permit for his planned demonstration after a Swedish court ruled that banning it would impinge on the right to freedom of speech.

The permit, however, did not allow him to burn objects, and Mr. Momika was subsequently charged with agitation against an ethnic or national group in four incidents of kicking, stamping on and burning a Quran. He also made speeches with derogatory statements directed against Muslims and Islam, according to the indictment.

“The fact that statements are made in a large square and disseminated is a prerequisite for incitement to racial hatred,” said Anna Hankkio, a Swedish prosecutor who initially brought the charges against Mr. Momika. “It is up to the district court to assess whether the burning of the Quran can also be considered incitement against a group of people.”

Later that summer, Mr. Momika again burned Qurans, according to the indictment.

The Quran burnings — and the resulting horror and outrage from the Muslim world — sparked debates in Sweden, which has struggled with whether to allow such protests.

Before Mr. Momika burned the holy book, Swedish authorities had denied other anti-Quran protests, citing concerns about disruption to public order. After the burning, Sweden’s foreign ministry called Mr. Momika’s action Islamophobic, and officials warned that such protests could affect the country’s national security policy. The domestic security agency briefly raised its terrorism threat to its most severe designation.

Salwan Najem, who joined Mr. Momika in some protests and was also accused of burning a Quran, was a co-defendant in the case that was to be decided on Thursday. He is now set to receive his verdict on Feb. 3, the Stockholm District Court said in a statement.

On Thursday, Mr. Najem expressed fear, posting a link on X to a story about Mr. Momika’s killing.

“I am next,” he wrote.

As he does every three months, Sibusiso traveled on Wednesday morning to a clinic in the capital of Eswatini, a tiny southern African nation, to get a refill of the H.I.V. medication he needs to save his life. When he arrived, the door was locked and about 20 other patients stood outside, baffled that the clinic was closed.

Sibusiso, 39 and unemployed, had heard rumors that President Trump was pulling funding for the program that supported his treatment. Now, though, he learned the reality: The Trump administration had ordered a halt to the President’s Emergency Plan for AIDS Relief, or PEPFAR, one of America’s most consequential aid programs in Africa.

The abrupt pause of a $6.5 billion program established by former President George W. Bush and credited with saving the lives of tens of millions of people sent patients, clinicians and public health advocates across Africa into a panic. Many feared a return to some of the darkest days on the continent, when H.I.V. spread rapidly and a diagnosis was akin to a death sentence.

As Sibusiso stood outside the clinic, he feared he could be next. He had taken the last of his antiretroviral medication that morning. And even though the Trump administration had backtracked, suddenly announcing on Tuesday that lifesaving medications and treatments could continue to be distributed, the clinic remained shuttered in the confusion.

Sibusiso, standing outside, had no idea where or when he could get more medicine.

“I’m now thinking of dying,” said Sibusiso, who requested that only his first name be used to protect his privacy. “What am I going to do without this treatment?”

The Trump administration has said that foreign assistance programs will be paused for three months as it reviews how money is being spent. If the administration decides to end PEPFAR, it could lead to 600,000 deaths over the next decade in South Africa alone, where the program has its largest number of beneficiaries, according to a study.

“The next 90 days are looking so dystopian,” said Nozizwe Ntsesang, the chief executive of a leading gay rights advocacy group in Botswana.

Across South Africa and other countries in the region, fear and uncertainty are palpable. Some African leaders had shared optimism and excitement about a second Trump term. But now, one of his first moves appeared to put lives at risk.

“I’m scared,” said a 19-year-old South African college student who was born with H.I.V. “People will die. It’s going back to the ’90s where people did not have enough medication to treat the disease.”

The student, who also requested anonymity to protect her privacy, said the clinic that she goes to in Johannesburg gave her a three-month supply of her antiretroviral medication on Wednesday instead of the usual six months. Officials explained that they wanted to reserve some stock in case other clinics ran short, she said.

PEPFAR does not provide medication for the South African health system, but it does employ around 13,000 medical professionals, from doctors to community health workers, who are responsible for ensuring that people are tested and seek proper treatment. Virtually all of those employees were ordered to stop working after the Trump administration froze foreign aid programs, according to health care advocates.

The staff shortages, health workers and rights groups said, led to much larger crowds at public clinics in South Africa, where roughly eight million people are living with H.I.V. and 5.7 million receive treatment.

Amid the chaos of the freeze and the Trump administration’s backpedaling, many clinics remained shuttered on Wednesday, with medical workers unsure about the new rules and patients frantic to secure their medication.

Some patients have been forced to wait 10 hours for treatment, advocates said. There were also fears that, without counselors to talk to, some patients, especially those newly diagnosed with H.I.V., would not administer their treatments properly or seek help in the future.

“The abrupt stop is not responsible,” said Solange Baptiste, the executive director of the International Treatment Preparedness Coalition, an organization that works to improve access to treatment for people with H.I.V. “Lives are at risk when you do that.”

South Africa is in a better position than many other African countries. The government procures most of its H.I.V. drugs directly and relies on PEPFAR for only about 17 percent of its overall H.I.V. treatment budget.

Neighboring Botswana, which has received nearly $72 million in aid from PEPFAR since 2003, also buys its own treatment medication, but the work and funding stoppage has weighed heavily on local organizations.

Stanley Monageng said he cried when he learned about the Trump administration’s order. Mr. Monageng, 78, has been running an organization in Molepolole, in southern Botswana, since 2005. It provides support for children with H.I.V. and relies mostly on PEPFAR funding, he said.

Mr. Monageng said he was worried all week that he would not be allowed to provide antiretroviral medication to the dozens of children, many of them orphaned, who rely on his organization for help. Mr. Monageng himself has been living with H.I.V. for 25 years and says he has personally benefited from the PEPFAR program.

“I asked myself, ‘How are these orphans going to survive? How am I going to help them?’” he said on Wednesday from the three-bedroom house that he uses for the center. “I’ve been surviving all these years because of America.”

At HealthPlus 4 Men, the clinic that was closed in Eswatini on Wednesday, officials encouraged anxious patients to go to a public hospital to seek medication. But most patients were uncomfortable with that option.

HealthPlus primarily treats gay men, a population that has been historically stigmatized in Eswatini. Many of its patients fear going to government-run facilities, where they worry they will face discrimination. Public hospitals also often provide prescriptions that many patients can’t afford to fill, said Sibusiso Maziya, the executive director of HealthPlus.

“It’s a sad moment for us,” Mr. Maziya said. “They want to know when this situation will change, when are we opening.”

Despite the waiver issued by the U.S. government on Tuesday, Mr. Maziya said his organization was continuing to withhold antiretroviral medication supplied with PEPFAR funds as it awaits clarity from its funders on what it is allowed to do.

Msizi Mkhabela, the operations manager for HealthPlus, added that the organization promotes diversity, equity and inclusion by supporting equal treatment for gay men. That mission could run afoul of the Trump administration’s freeze on such programs and may put the clinic at a higher risk of being permanently defunded.

In addition to medication, HealthPlus also has a mobile clinic and outreach programs to make sure that people living in rural areas are being tested and receive treatment for H.I.V. The organization considers those programs an essential part of its efforts to prevent the spread of the disease. But all of that was put on hold because the funding came from PEPFAR and HealthPlus is unsure what activities are allowed to continue.

“We are literally shaking and worried,” Mr. Mkhabela said. “Very much frustrated.”

Reporting was contributed by Yvonne Mooka from Molepolole, Botswana, Lynsey Chutel from London and Golden Matonga from Blantyre, Malawi.

Internal political tensions in Ukraine have been rising in anticipation of a cease-fire that might lead to elections. This week, they burst into the open with a striking public rebuke of President Volodymyr Zelensky by the mayor of Kyiv.

In a video address issued on Wednesday, the mayor of the country’s capital, Vitali Klitschko, accused the president’s office of abusing the powers of martial law, the latest salvo in a continuing dispute over the use of military rule during the nearly three-year war against Russia.

Mr. Klitschko, a former heavyweight boxing champion who has built a political base in the capital, has engaged in a low-boil feud with Mr. Zelensky for several years, chafing at what he views as the president’s attempt to usurp the authority of the city.

In his statement, Mr. Klitschko accused Mr. Zelensky of appointing a military administrator for the city who he said had tried to assume the powers of the elected City Council.

The administrator, Tymur Tkachenko, was appointed as the martial law chief of Kyiv on Dec. 31. He was part of a round of appointments in regions and cities across Ukraine that began in 2022 and were intended to bolster defenses by giving authority to officers in the military chain of command over local governments.

Mr. Klitschko said Mr. Tkachenko had no military background, which he said “indicates political motives for this appointment.” He accused Mr. Tkachenko of “interference in and blocking of economic activity” in the capital by delaying decisions on infrastructure and construction unrelated to the war.

“While you, as the supreme commander in chief, are focused on the war and the defense of Ukraine, people around you are tirelessly engaged in political intrigue,” Mr. Klitschko said in a video addressed to Mr. Zelensky.

The presidential office did not immediately respond on Thursday to a request for comment about Mr. Klitschko’s accusation.

Mr. Tkachenko issued a combative response to the accusations, saying that he did not see any scope for constructive dialogue with Mr. Klitschko and that the military administration would therefore “solve the city’s problems and help Kyiv residents.”

The feud has escalated at an awkward time for Ukraine, as it waits to see whether President Trump continues American support to Kyiv or tries to forge cease-fire terms with President Vladimir V. Putin of Russia that could be favorable to the Kremlin.

Under martial law introduced when Russian forces invaded in February 2022, frontline towns and cities in Ukraine are governed solely by military administrations. Many of those farther from the front line have both civilian and military authorities.

Civil society groups in Ukraine have long been raising concerns that the central government uses military administrators to secure a stronger grip on authority, even on issues not directly related to defense. The move comes against a backdrop of a preinvasion setback for Mr. Zelensky’s political party in local elections that left opposition politicians in control of most cities and regional governments, including in Kyiv.

In the last local elections before the invasion, the president’s party, Servant of the People, did not win a single mayoral position in Ukraine. Yet today under martial law, one-third of the heads of local and regional military administrations appointed under martial law in Ukraine have ties to Servant of the People.

The expectation is that if a cease-fire is achieved, Ukraine would lift martial law and hold elections; the last presidential election occurred in 2019, when Mr. Zelensky took office. Mr. Klitschko is considered a potential competitor to Mr. Zelensky in a presidential election, though he has not declared an intention to run.

Mr. Klitschko has been mayor of Kyiv since 2014. In his video criticizing Mr. Tkachenko, the appointed military administrator, he accused him of failing to review documents on “orders to restore buildings, compensate owners for damaged facilities, restore infrastructure and many other things.”

He added that the main tasks of the military administration should concern drafting men to serve in the army, civil defense, public safety and the protection of critical infrastructure.

The conflict in Kyiv comes amid criticism from opposition lawmakers that Mr. Zelensky has used martial law powers to enhance the authority of a close circle of advisers, as well as to clear out political opponents in local government.

In 2022 after the full-scale invasion, for example, the elected mayor of the city of Chernihiv, north of the capital, said the presidential office was trying to remove him and appointing a military administrator in his place.

The tension between that mayor, Vladyslav Atroshenko, and the Zelensky administration predates the war, political analysts say, when the mayor decided to collaborate with Mr. Klitschko’s opposition political party, UDAR, which means “Punch.” Mr. Atroshenko was later stripped of his powers as mayor in a court decision in a case accusing him of conflicts of interest.

In December last year, the acting mayor of Chernihiv, Oleksandr Lomako, resigned and also posted a video address to Mr. Zelensky accusing the military appointee of abusing powers. He said the military administrator had taken the city hostage.

Elections can only be held after martial law is lifted.

Analysts say that the largest problem in the relationships between military and civil administrations is the duplication of powers. It was not always the case.

Initially, when Mr. Zelensky created the Kyiv City Military Administration in February 2022, Mr. Klitschko as mayor automatically became its head. But later, to “improve the capital’s defense,” Mr. Zelensky said, he split the two roles, with Mr. Klitschko staying on as mayor, and a general, Mykola Zhernov, taking charge of the parallel military administration office for the city.

Members of Mr. Klitschko’s political party serving on the City Council regularly raise questions about the appropriateness of operating a separate military administration in the city after the Russians were pushed back from the capital nearly three years ago and the city became relatively well protected from missile strikes with air defenses.

On Oct. 4, 2019, a 13-year-old British boy called a child welfare hotline from his home in Banks, a village in northwest England, and asked: “What should I do if I want to kill somebody?”

The teenager, Axel Rudakubana, said that he had started taking a knife to school because he was being bullied. After counselors from the hotline called the police, he told officers that he thought that he would use the weapon if he became angry.

It was the first of several warnings about Mr. Rudakubana, now 18, and his increasingly violent tendencies. But five years after that call, on July 29 last year, he was able to commit one of the worst attacks on children in recent British history, murdering three girls at a Taylor Swift-themed dance class in Southport, a town near Banks, and attempting to kill eight other children and two adults who tried to protect them.

Last week Mr. Rudakubana was sentenced to life in prison, bringing a small degree of closure to the atrocity that provoked outrage across Britain. In other ways, however, the reckoning has only begun, as the country faces profound questions raised by the attack.

How did he slip through the nets of multiple agencies — including a counterterrorism initiative called Prevent, to which he was referred three times? How should the authorities deal with young people who become fixated on violence for its own sake, rather than in service of Islamist or other extremist ideologies, and who access a torrent of graphic content and encouragement online? And do laws crafted in the wake of the terrorist attacks of Sept. 11, 2001, “need to change to recognize this new and dangerous threat,” as the British prime minister, Keir Starmer, suggested last week?

‘Poisonous Online Extremism’

In police interviews, Mr. Rudakubana refused to give any motive for his knife attack. The ensuing riots that broke out across England were fueled by false claims that it was an act of Islamist terrorism committed by a recently arrived undocumented migrant.

In fact, Mr. Rudakubana was a British citizen, born in Wales to a Christian family from Rwanda. At his sentencing last week, the prosecutor, Deanna Heer, said: “There is no evidence that he ascribed to any particular political or religious ideology; he wasn’t fighting for a cause. His only purpose was to kill.”

The police later found 164,000 documents and images across his digital devices, including images and videos of dead bodies, torture and beheadings, demonstrating a “longstanding obsession with violence, killing and genocide,” Ms. Heer said.

His research spanned a chaotic range of conflicts, including those involving Nazi Germany, Gaza, Ukraine, Sudan and the Balkans. He had also downloaded an Al Qaeda training manual which included knife attack methods. He had made ricin, a biological toxin, and kept it in a plastic lunchbox under his bed.

Teachers concerned about his interest in violence had reported him to Prevent three times, when he was 13 and 14. Prevent, which started in 2003, aims to identify people who show early signs of terroristic leanings and divert them from violence before it happens. But its focus is on ideology, and after each referral of Mr. Rudakubana, officials closed the case because he appeared to lack any ideological motivation.

Diagnosed with autism at 14, he had become increasingly reclusive, anxious and aggressive in the years before the attack. He received mental health treatment for four years but “stopped engaging” with clinicians in 2023, officials said in a statement. But his defense lawyer said there was “no psychiatric evidence which could suggest that a mental disorder contributed” to his actions.

Counterterrorism officials have warned for some time that they are seeing more individuals with amorphous, ill-defined extremist traits. Ken McCallum, the head of MI5, Britain’s domestic security service, said last year that “very young people are being drawn into poisonous online extremism,” and that would-be terrorists had a “dizzying range of beliefs and ideologies.”

Earlier this month, another British teenager, Cameron Finnigan, was sentenced to jail after being part of an online Satanist group with neo-Nazi links called 764, which has been the subject of a public warning by the F.B.I. The group blackmails other children into filming or livestreaming self-harm, violence and sexual abuse. Mr. Finnigan, 19, used the Telegram app to encourage contacts to commit murder and suicide.

And in 2021, a 22-year-old man, Jake Davison, murdered his mother in Plymouth, England, before roaming the streets with a shotgun and killing a three-year-old girl, her father and two other passers-by before killing himself. Mr. Davison was immersed in online communities of incels — so-called “involuntary celibates” who blame women for their perceived inability to form relationships.

Like Mr. Rudakubana, Mr. Davison had previously been reported to the Prevent program. A careers adviser who made the referral told an inquest that a Prevent official had said Mr. Davison did not meet the criteria for intervention.

While each case was unique, in all three, isolated young men were able to access a wealth of material online glorifying mass murder, and then encouraged or carried out real world violence. Yet none would fit neatly into Britain’s current definition of terrorism, which requires a purpose of “advancing a political, religious, racial or ideological cause.”

Britain’s Home Office, which oversees Prevent, said that in the case of Mr. Rudakubana, “opportunities were missed to intervene,” and Mr. Starmer has announced an inquiry into “our entire counterextremist system,” saying he understood why the case made “people wonder what the word ‘terrorism’ means.’”

But proposals to expand the definition of terrorism are contentious. Jonathan Hall, Britain’s independent reviewer of terrorism legislation, warned in an opinion article last week that broadening the definition to include “violence clearly intended to terrorize,” as Mr. Starmer suggested, would risk “too many false positives.” He also worried it would stretch counterterror resources. Mr. Hall called instead for “a wholly new capability to deal with those motivated by noninstrumental extreme violence.”

‘Mixed, Unclear and Unstable Ideology’

Islamist terrorism remains the largest security threat facing Britain, responsible for approximately 75 percent of counterterrorism work by M15, the agency says, while extreme right-wing terrorism is responsible for most of the rest.

But Vicki Evans, the U.K.’s senior national coordinator for counterterrorism policing, acknowledged that authorities had been grappling with an emerging cohort of people that the Prevent program labeled “mixed, unclear and unstable ideology,” which Mr. Rudakubana fell into. “There are a growing number of young people with complex fixations with violence and gore in our casework, but with no clear ideology other than that fascination,” she said.

Prevent has since split the “mixed, unclear and unstable” category into several parts, including incels and school shooting obsessives. But almost one in five people referred in the year to March 2024 were still simply categorized as “conflicted.”

Gina Vale, a University of Southampton criminologist who studies teenage terror offenders, said the trend has grown internationally for several years. “There are less clearly defined ideological fault lines, particularly among young people — that’s a reality that we now need to adapt to,” she said.

A 2024 study of 140 convicted terrorists in England and Wales found that 57 percent of lone attackers had some form of “mental illness, neurodivergence or a personality disorder,” and that the internet was “found to play an important role in radicalization pathways and attack preparation.”

Teenage terror offenders are often socially isolated, Dr. Vale said, and for many, “violence in whatever form is seen to be the answer — to gain status, to connect with a network, to have a feeling of belonging, to seek revenge, whatever it is.”

A review into Prevent’s response to Mr. Rudakubana is set to be published within days. Yvette Cooper, the home secretary, has already told Parliament that the review concluded that “too much weight was placed on the absence of ideology” without considering his obsession with extreme violence.

But amid the debate over whether his attack could have been prevented, experts note that a small subset of individuals have always been capable of appalling violence.

“People don’t need a coherent worldview to embark on mass violence,” said Tim Squirrell, who researches violent movements at the Institute for Strategic Dialogue, a research institute in London. “We cannot prevent every single case but we need to be looking at mass violence as a problem in itself rather than as a subset of terrorism.”