The Islamic terrorist who wounded 10 people during a September attack at a Minnesota mall used a pair of steak knives to stab his victims in the head, neck and chest while frantic shoppers hid and workers struggled to close store gates, the FBI revealed during a Thursday news conference.

Dahir Ahmed Adan, 20, was shot and killed by an off-duty police officer who had been shopping at a Bath & Body Works as the Sept. 17 incident unfolded. Video footage released by the FBI and tweeted out by a Minneapolis Star Tribune reporter showed Adan’s final moments, the extremist crawling in a pool of blood – still armed with a knife – toward Officer Jason Falconer. Adan, armed with a knife in each hand, previously had charged Falconer twice. Falconer’s shooting was deemed justified and he will not be charged, officials said.

“We are very grateful that off-duty police officer was in the mall that night,” St. Cloud Mayor Dave Kleis said.

Authorities believe Adan had been radicalized recently. They said he had flunked out of school and lost interest in his typical hobbies before turning more deeply to Islam. The FBI was trying to unlock Adan’s phone and was still working to figure out if he self-radicalized or was radicalized by others.

"We were told (he) had not previously shown an interest in religion," FBI Special Agent Rick Thornton said.

Adan yelled Islamist phrases during the attack and, at one point, approached Falconer and asked him if he were Muslim, investigators said. That encounter preceded the foot chase and shooting that ended in Adan’s death.

"We have numerous credible witness accounts of him asking victims during the attack if they were Muslim and at least one instance yelling 'Allahu akbar' while stabbing one of his victims and others heard him yelling ‘Islam Islam’ during the attack," Thornton said.

Falconer ultimately fired 10 shots, hitting Adan six times. After killing Adan, Falconer showed his police badge to horrified shoppers who were unsure of what was unfolding in front of them.

While driving to the mall, Adan struck a cyclist – who rolled across the car’s hood. Adan did not stop and later ran a red light en route to his planned attack.

FBI Director James Comey said last week it appeared Adan was at least partly inspired by extremist ideology. When the attacks happened, the Islamic State-run news agency claimed Adan was a "soldier of the Islamic State" who had heeded the group's calls for attacks in countries that are part of a U.S.-led anti-ISIS coalition. It wasn't immediately known whether the extremist group had planned the attack or knew about it beforehand.

The Associated Press contributed to this report.