A former leader in the FBI said Wednesday night the agency was "back to square one" after authorities released a "subject" who had been taken into custody in connection with the killing of conservative activist Charlie Kirk.

Kirk, 31, was the CEO and co-founder of Turning Point USA, a conservative student organization. He was shot in the neck during an event at Utah Valley University.

FBI Director Kash Patel announced the agency had a suspect in custody just a few hours after the shooting. However, media reports indicate that the authorities let that person go.

Andrew McCabe, the former FBI deputy director, joined CNN's Anderson Cooper on "AC360" on Wednesday to discuss the case.

"They're really back at square one with the release of the person of interest," McCabe said. "So, they are back to assessing what they believe the shooter's perch to have been, whether that's the space on the roof that we've seen, not really roped off. We haven't seen a whole lot in terms of evidence collection there."

"And if not, then they should be looking at every single vantage point that could have been used," McCabe said.

Watch the entire clip below or by clicking here.