DETROIT — The man charged with stabbing a police officer at the Flint airport in a possible act of terrorism was a part-time caretaker at the Montreal apartment building where he lived and had once studied to sell insurance, people who knew him said Thursday.

Amor Ftouhi kept the building stairwells clean and always paid his rent on time, his landlord told The Associated Press. The 49-year-old from Tunisia lived in a two-bedroom apartment with his wife and children and “never made any trouble,” Luciano Piazza said.

Investigators are working to learn more about Ftouhi, whom they describe as a lone-wolf attacker who made his way from Canada to the seemingly random destination of Flint, a struggling Michigan city once known for its sprawling General Motors factories but now better known for lead-tainted water.

Once in the U.S., he unsuccessfully tried to buy a gun, but instead managed to buy a knife, David Gelios, head of the FBI in Detroit said Thursday. He did not elaborate.

The attack Wednesday at Bishop International Airport, about 50 miles (80.46 kilometers) northwest of Detroit, was being investigated as an act of terrorism, but authorities said they have no indication that the suspect was involved in a “wider plot,” Gelios said.

Ftouhi, a dual citizen of Canada and Tunisia, stabbed airport police Lt. Jeff Neville with a large knife after yelling “Allahu akbar,” the Arabic phrase for “God is great.” According to the FBI, Ftouhi said something similar to “you have killed people in Syria, Iraq and Afghanistan, and we are all going to die.”

Ftouhi was immediately taken into custody and was charged in a criminal complaint with committing violence at an airport. Acting U.S. Attorney Dan Lemisch says more charges are coming in the days ahead. Ftouhi is in custody and has a bond hearing scheduled for Wednesday.

Ftouhi wanted to identify an international airport, but, Gelios said, authorities “have absolutely no indication that he had any association with anyone in the Flint area or, thus far, in Michigan.”