(NewsNation) — The Islamic State group claimed responsibility for the attack on a suburban Moscow concert hall that killed at least 133 people. Former FBI senior executive Josh Skule joined NewsNation’s “Morning in America” to discuss how Russia is likely to proceed.

“The priority is to actually arrest those who are responsible. Unfortunately for us, Russia is not a trustworthy media source. So they will be the reports coming out should be looked at with a critical eye,” Skule said.

Putin said authorities have detained a total of 11 people in the attack, which also injured more than 100 concertgoers and left the venue on Moscow’s western rim a smoldering ruin.

He called it “a bloody, barbaric terrorist act” and said Russian authorities captured the four suspected gunmen as they were trying to escape to Ukraine through a “window” prepared for them on the Ukrainian side of the border.

“This is a typical terrorist attack. They are going in to just maim, kill, destroy, indiscriminate. They don’t care about soft targets, which this clearly was, civilian casualties. They’re not looking to attack a military target. They’re looking to kill, unfortunately, civilians,” Skule told NewsNation.

The attack, the deadliest in Russia in years, is a major embarrassment to the Russian leader and happened just days after he cemented his grip on the country for another six years in a vote that followed the harshest crackdown on dissent since the Soviet times.

The Associated Press contributed to this report.