Images of the September 17 were released Thursday after authorities concluded that the officer, Jason Falconer, would not face criminal charges in the case.
Stearns County Attorney Janelle Kendall said Falconer's actions were "justified and lawful."
"Reacting as either as a licensed peace officer or as an average citizen under these circumstances, deadly force was legally authorized," she said.
Kendall also said that "during all aspects of this encounter, Falconer engaged Adan from the perspective of a police officer, albeit off-duty," by showing Adan and others his badge multiple times.
Adan stabbed 10 people at the Crossroads Center mall in St. Cloud, Minnesota. All 10 survived the attack.
The video, a compilation of images from closed-circuit security cameras in the stores where the stabbings occurred, shows Adan, dressed in private security uniform, first walking into an electronics store and chasing an employee, stabbing him repeatedly.
He then headed to a candy store, a knife in each hand.
After being denied entry by a quick-thinking employee who pulled down a metal gate, Adan headed to Macy's.
Falconer followed him into Macy's after hearing the commotion. He repeatedly shows his badge to Adan and those around him while pointing his gun at the suspect. Police say Adan initially got down on the ground, still holding onto the knives, before getting up and and charging at Falconer and others. That's when Falconer shot him.
In a news conference Thursday, FBI Special Agent Richard Thornton said there's enough evidence to suggest the attack was premeditated. Thornton said Adan, who worked as a private security guard, called his boss shortly before the stabbings to inform him that he wouldn't be coming into work. Adan then headed to a convenience store where he was a regular customer and told employees, "You won't be seeing me again."
Thornton says Adan also committed a hit-and-run on the way to the mall, striking a bicyclist.
Several witnesses describe Adan asking victims if they were Muslim before stabbing them, Thornton said. He was also heard screaming "Allahu Akbar," or "God is great" in Arabic, and "Islam, Islam, Islam" during the stabbings, the agent added.
Was radicalism to blame?
Authorities say Adan may have been radicalized before the attack. Thornton said the young man had become more religious within the past few months and withdrew from his network of friends.
"He went from being an excellent student with a high GPA to flunking out of college almost overnight. Some of his friends noticed he would become agitated at things which in the past would not have bothered him."
"These behaviors individually may not be significant, however, the totality of Adan's behavior and the actions suggest he may have been radicalized either with the influence of others or on his own," Thornton explained.
While Adan's interest in Islam isn't enough evidence to suggest radicalization, Thornton said, his actions "were consistent with (those of) radical Islamic groups."
Falconer was the former police chief of Albany, Minnesota. Now, he works as a part-time officer with the Avon Police Department.
He was in the mall shopping that day, and happened to be in the "right place at the right time," St. Cloud Mayor Dave Kleis said last month.
"He protected others from being injured and potentially loss of life. Clearly, a hero."