Editor's note: This video contains graphic content. Authorities release graphic videos that show Dahir Adan stabbing people in the Minnesota shopping mall attack before being killed by an off-duty police officer. (Reuters)

He chased one store clerk into an electronics store, swiping at his head with a pair of steak knives, and then plunging one into his back before the man was able to scramble to his feet and run. He came within inches of stabbing another store clerk, who pulled a metal shutter closed just in time. He lunged repeatedly at an off-duty police officer who had chased him, near the end, into a Macy’s store. And then, even after he was shot, he got to his feet and lunged a second time.

The FBI and Minnesota law enforcement officials for the first time on Thursday released surveillance video footage that show the mall attack by Dahir Adan, a 20-year-old from St. Cloud, Minn., on Sept. 18.

Ten people, including a pregnant woman, were injured in the attack at the Crossroads shopping mall, a five-minute drive from Adan’s house. But the incident, which left Adan dead, also left a typically quiet town with a flood of unanswered questions and an equally sizable flood of rumors to fill the void.

FBI Special Agent Rick Thornton said Thursday that the agency’s ongoing investigation has so far revealed a young man who appears likely to have become “radicalized” by extremist ideology. Thornton and local authorities said they decided to release the surveillance videos of the attack, along with new details of Adan’s rampage and his potential motivations, in the interest of transparency.

Adan, who had moved to the United States from Kenya with his family as a child and had grown up in St. Cloud, had withdrawn and shown an increased interest in religion in the months leading up to the attack, Thornton said. Like his family, Adan was Somali American.

“Within the last several months, Adan became interested in Islam and began reading the Koran. We are told that Adan had not previously shown interest in religion,” he said.

Thornton, who said that investigators had so far conducted more than 180 interviews, as well as searches of physical locations, Adan’s computer and other electronic devices, cautioned that increased religiosity is not an indicator, on its own, of a shift toward violent extremism. But he said that the religiosity coupled with other character changes and Adan’s behavior on the night of the attack suggested that he may have been moved by extremist thinking.

“There are reports he withdrew from his network of friends. He became less interested in playing basketball and Xbox. . . . He went from being an excellent student to almost flunking out of college overnight,” Thornton said.

Adan was also behaving strangely on the day of the attack. He left his job as a private security guard and came home at 3 p.m. on a day he was supposed to work until 10 p.m. He never changed out of his security guard uniform, as he typically would. And when a convenience store employee, where Adan was a regular, said “See you later,” Adan responded, “You won’t,” Thornton said.

Adan arrived at the mall armed with two steak knives, which officials showed in pictures to reporters on Thursday. At the mall, Adan asked some of his victims, including the off-duty police officer who would ultimately shoot him, whether they were Muslim. And “at one point yelled ‘Allah [sic] Akbar,’ ” Thornton said. “Others heard him yelling ‘Islam, Islam’ during the attack.”

There was no sound in the videos released by law enforcement Thursday, which officials said was due to the fact that the footage came from cameras that are normally meant to detect shoplifters.

Somali Americans who were close to Adan had previously raised questions about witness claims of the attack, and questioned whether Adan was not, in fact, provoked, or whether he was even the victim of a police conspiracy.

An attorney who spoke on behalf of the family Thursday disputed the FBI’s assertion that Adan had shown noticeable behavioral changes, including an increased religiosity. “They did not notice at all, and they do not believe evidence was presented that established that,” said Abdulwahid Osman, the attorney.

“Nothing that was presented also produces any evidence that links Dahir to any local or global terrorism,” Osman added. He said Adan’s family is continuing to cooperate with law enforcement, and is mourning what they consider “a very, very tragic event.” But, “they are looking for answers.”

“Nothing that was presented today answered the question of why, what led this incident to occur?” Osman said.

Officials told reporters on Thursday that there was no evidence that Adan was provoked. Extensive witness accounts and surveillance video show that Adan started his attack outside the mall, and then chased victims on a path through the mall’s hallways before ending in Macy’s. “There is compelling evidence to suggest that this was a premeditated attack on behalf of Dahir Adan,” Thornton said.

On the way to the mall, Adan was also involved in a hit-and-run with a bicyclist, he said.

Minnesota’s Somali-American community, most of them refugees and the descendants of refugees from the country’s civil war in the 1990s, have a history of tension with local law enforcement and the FBI, whom they accuse of discrimination and entrapment. The FBI says that more than two-dozen young people from the Twin Cities have left the country to join extremist groups abroad over the past 15 years.

The FBI has not identified any Somali Americans from St. Cloud, which is 65 miles northwest of Minneapolis, who have traveled to fight in foreign wars. If Adan was, in fact, motivated by terrorist ideology, he would be the first to launch an attack in Minnesota.