What we know about the killing of Charlie Kirk

- At a university -

Kirk, the head of the largest conservative youth movement in the United States, which he co-founded in 2012 at the age of 18, was speaking around noon on the campus of Utah Valley University.

Dressed in a white t-shirt with the word "Freedom" across the front, Kirk sat in a chair under a tent as he answered questions from the large audience gathered around him.

The event was the first of about 15 scheduled across the country through the end of October.

- A gunshot, then screams -

Former Utah congressman Jason Chaffetz, who was at the event, told Fox News that Kirk was responding to a question about "transgender shooters, mass shooters, and in the midst of that, the shot rang out."

The 31-year-old collapsed and blood spurted from his neck, according to a video clip shot from a nearby location.

Kirk was then rushed away on a stretcher by his security detail.

"As soon as that shot went out, he fell back," Chaffetz said. "Everybody hit the deck... a lot of people started screaming, and then everybody started running."

- Manhunt for killer ongoing -

Authorities have not arrested a suspect in Kirk's shooting, described as a "targeted attack" in a statement from Utah's Department of Public Safety.

"The shooter is believed to have fired from the roof of a building down to the location of the public event in the student courtyard," it said.

Two men were briefly detained and released after being questioned by law enforcement officials as the manhunt continued.

One man, George Zinn, was charged with obstruction.

Neither man has "current ties to the shooting," authorities said.

- Trump announces Kirk's death -

Trump announced Kirk's death, writing on his Truth Social platform: "The Great, and even Legendary, Charlie Kirk, is dead."

On the other side of the political spectrum, Democratic figures also condemned the shooting, including Kamala Harris, who said that "political violence has no place in America."

- Trump vows crackdown -

Although a suspect has not yet been identified, Trump linked rhetoric from the "radical left" to Kirk's killing and vowed to carry out a crackdown.

"This kind of rhetoric is directly responsible for the terrorism that we're seeing in our country today," he said in a somber four-minute video, seated at the Resolute Desk in the Oval Office.

"My administration will find each and every one of those who contributed to this atrocity, and to other political violence, including the organizations that fund it and support it," the US president said.