Charlie Kirk, an influential conservative activist and a close ally of US President Donald Trump, was shot dead while speaking at an event at a university in Utah.
There is still a lot that is unclear about the incident but here is what we do know.
What happened?
Kirk, 31, who had been invited to speak at Utah Valley University (UVU), was seated under a white gazebo addressing a crowd of about 3,000 people in the quad, an outdoor bowl courtyard.
According to eyewitnesses and videos taken at the scene, he was responding to a question about gun violence when a single shot rang out around 12:20 local time.
Kirk can be seen recoiling in his chair, with blood visible on his neck, before the terrified crowd starts running.
"I heard a loud shot, a loud bang and then I saw his body actually - in slow motion - kind of fall over," one eyewitness told reporters.
"We all dropped to the ground, and I want to say we sat like that for about 30 to 45 seconds, and then everyone around us got up and started running," said Emma Pitts, a reporter from Deseret News.
Kirk was rushed to hospital in a private vehicle. Hours later, Trump confirmed his death on a post on Truth Social.
The university campus has since been evacuated, as authorities search for the shooter.
Kirk's wife and two children were at the scene, but are safe. No-one else at the event, or on campus, was injured.
Who is the suspect?
Authorities say this was an assassination - but we don't know yet who shot Kirk, or why.
Two people were arrested in the hours after the incident and later released. They have "no current ties" to the shooting, Utah officials have said.
"This shooting is still an active investigation," the Department of Public Safety, which covers law enforcement in the state, said in its latest update.
A massive manhunt is under way for the shooter. The campus has been locked down and heavily-armed police are going door-to-door as part of the search, the BBC's Regan Morris reports from the campus.
Law enforcement officials say the killer is believed to have fired the fatal shot from the roof of a building that is located near the courtyard where Kirk was speaking.
They say they are going through CCTV footage, and believe the suspect was "dressed in dark clothing".
BBC Verify has been examining videos posted on social media, which people claim show a "shooter" on the roof of a university building after the attack.
It was posted on X after the shooting, but we cannot verify when it was filmed.
The poor quality of the video makes it hard to determine what the dark shape pictured in it might be. Based on the building's characteristics, the BBC was able to identify it as UVU's Losee Center - a campus spokesperson has said the shot came from there.
Who was Charlie Kirk?
As an 18-year-old in 2012, he co-founded Turning Point USA (TPUSA), a student organisation that aims to spread conservative ideals at liberal-leaning US colleges.
He became known for holding open-air debates on campuses across the country, fielding rapid-fire questions in a signature "change-my-mind"-style - just like he was doing on Wednesday when he was shot.
His social media feed and daily podcast offer a snapshot of what he often debated - the issues ranged from gun rights and climate change, to faith and family values.
Kirk had many critics who saw him as a divisive figure that promoted controversial and, at times, conspiratorial beliefs.
But he also had his fans, for whom he was a champion of free speech. They credit him with playing a key role in convincing younger voters to turn out for Trump in last year's election. He was valued within the Trump administration for his keen understanding of the grassroots Maga (Make America Great Again) movement.
What has the reaction been?
"The Great, and even Legendary, Charlie Kirk, is dead. No-one understood or had the Heart of the Youth in the United States of America better than Charlie," Trump said in a statement on Truth Social.
"He was loved and admired by ALL, especially me," the president added, ordering that all flags be flown at half-mast across the country.
Former US presidents have offered their condolences. Joe Biden, Trump's predecessor, said there is "no place in our country for this kind of violence", while Barack Obama called the shooting a "despicable act", and said his family was praying for Kirk's loved ones.
Several key White House officials expressed their sorrow, including Health Secretary RFK Jr and Secretary of State Marco Rubio.
UK Prime Minister Kier Starmer offered his sympathy in a statement: "We must all be free to debate openly and freely without fear."
Italy's Prime Minister Girogia Meloni said the "atrocious murder" was "a deep wound for democracy" while Argentinian President Javier Milei paid tribute to Kirk as "a formidable disseminator of the ideas of freedom and staunch defender of the West".
Is political violence in the US increasing?
In the first six months of this year, the US has experienced about 150 politically-motivated attacks.
That is nearly twice as many as over the same period last year, an expert told Reuters news agency.
Mike Jensen - from the University of Maryland, which for more than 50 years has tracked political violence in a database - said the US is in a "a very, very dangerous spot right now".
"This could absolutely serve as a kind of flashpoint that inspires more of it."
Kirk's murder is the latest in a string of high-profile attacks against political leaders in the US, including two attempted assassinations on Trump during his 2024 election campaign.
The president was injured in the ear after he was shot at a rally in Butler, Pennsylvania, last July and authorities say they thwarted a second attempt on his life at his West Palm Beach golf course two months later.
From the Oval Office on Wednesday night, Trump said "radical left political violence has hurt too many innocent people".
Comments like these – which he has made regularly – have stirred controversy. Critics say they neglect to acknowledge that the spate of violence is affecting left-leaning politicians too, and could incite further attacks against Trump's political opponents.
In June, Minnesota's top Democratic legislator and her husband were murdered in their home.
In April, Pennsylvania governor Josh Shapiro's house was burned in an arson attack, while the Democrat and his family slept inside.
Other incidents this year include politically motivated fire attacks on Tesla dealerships and the killing of two Israeli embassy staffers in Washington.
In 2022, the husband of then-House Speaker Nancy Pelosi was bludgeoned with a hammer after a man broke into the couple's home looking for the top-ranking Democrat with the intention of taking her hostage.
"The horrific shooting today at Utah Valley University is reprehensible," Pelosi said in a post on X on Wednesday.
Former US representative Gabby Giffords – who survived being shot in the head during a meeting with constituents in 2011 – also condemned the attack.
"Democratic societies will always have political disagreements, but we must never allow America to become a country that confronts those disagreements with violence."
