"They have the person that they wanted. So you have breaking news," Trump said on Fox News.
The president also expressed hope that the killer would be sentenced to death.
"I hope he's going to be found guilty, I would imagine, and I hope he gets the death penalty," Trump said.
Trump noted that he's unsure whether Charlie Kirk's killer acted alone or was part of a larger group.
Trump said that someone close to Charlie Kirk's alleged killer tipped off law enforcement.
"Somebody close to him turned him ... It happened with others. Somebody this close recognizes even a little tilt of the head, which nobody else would do, and somebody that was very close to him, said, that's him," Trump said.
He also called for quick trials in the United States.
"One thing I say, we have to have quick trials. I call it quick trial because in China, they do have quick trials. You know, they don't wait six years and China," Trump told Fox News, discussing the possible death penalty for the killer of US conservative activist Charlie Kirk.
Kirk died in hospital after being shot in the neck at an event at Utah Valley University on Wednesday. Trump called his murder a dark moment for the nation and vowed to find those responsible.
"I heard enough. I didn't want to watch it ... I didn't want to remember Charlie that way. But, yeah, it's horrific," Trump said.