Federal agents say they thwarted a planned terrorist attack on the Mall of America — the Bloomington, Minn., complex that ranks as the largest shopping mall in the United States and one of the country's most-visited attractions — this week, arresting an 18-year-old Minnesota man moments after he bought an assault rifle and ammunition in an undercover sting operation.

Sheikhdoon Abdullahi Mohamud, 18, had been under investigation for nearly two years, during which he traded text messages with a confidential informant, authorities said Wednesday. Tuesday, according to the criminal complaint, he paid $600 to an undercover FBI employee posing as a member of ISIS in exchange for an AK-47 and 200 rounds of ammunition — and agents arrested him on the spot in a public park in Richfield, several miles northwest of the mall. Undercover stings built around informants and fictitious ISIS contacts have been a recurring feature of federal counterterrorism work for more than a decade, with cases typically moving to arrest once a suspect takes a concrete step toward obtaining weapons.

“This was a radicalized young man who needed to be watched,” U.S. Attorney Daniel Rosen said, praising the FBI investigation. Agents “were able to detect a threat, and disrupt it, before the defendant carried out his intention to kill, in his words, maybe 30 to 60 people.”

Mohamud appeared in a yellow jail uniform for his initial hearing Wednesday in federal court in St. Paul. It was not immediately known whether the teen has an attorney who might speak on his behalf, and The Associated Press could not immediately identify any of his family members to contact for comment.

According to the complaint, Mohamud repeatedly affirmed in his messages with the informant that he intended to carry out an attack to kill non-Muslims at the mall on Oct. 24 — roughly two and a half weeks after his arrest — the date of a scheduled Hmong arts celebration. He also expressed admiration for recent terror attacks and an interest in traveling to Somalia to join ISIS, prosecutors said, but ultimately concluded he could not afford the trip and chose to attack the mall instead. Rosen said Mohamud is an American-born U.S. citizen of Somali descent.

The teen first came to the FBI’s attention in December 2024, the same month the informant began exchanging messages with him, the complaint said. By May 2025, agents were concerned enough to visit his home. His mother told them he was not yet home from school and called the boy’s father, who declined to speak with agents and said he would pass their contact information to his lawyer, according to the filing.

“What I would say to parents all over Minnesota, and all over America: If you get any indication — especially if you hear from federal law enforcement — that your son or daughter is being radicalized, to the point where federal law enforcement wants to come and give you that warning, those are warnings that ought to be heeded,” Rosen said.

Minnesota is home to tens of thousands of people of Somali descent, a community that has grown since refugees began arriving in the 1990s. Over the years, several state residents have been charged with attempting to join ISIS or other terrorist organizations.

This story was originally featured on Fortune.