BOSTON » Boston police said they have video showing a man who was under 24-hour surveillance by terrorism investigators lunging with a knife at a police officer and an FBI agent before he was shot and killed.

A law enforcement official with knowledge of the investigation said Usaama Rahim had been making threats against law enforcement. The official was not authorized to release details of the investigation and spoke on the condition of anonymity.

Police Commissioner William Evans said members of the Joint Terrorism Task Force approached Rahim in the city’s Roslindale neighborhood Tuesday morning to question him about "terrorist-related information" they had received when he went at officers with a large military-style knife.

Evans said officers repeatedly ordered Rahim to drop the knife but he continued to move toward them with it. He said task force members fired their guns, hitting Rahim once in the torso and once in the abdomen. Rahim, 26, was taken to a hospital, where he was pronounced dead.

Late Tuesday, the FBI arrested a man in connection with the case. Christina DiIorio-Sterling, a spokeswoman for U.S. Attorney Carmen Ortiz, said David Wright was taken into custody at his home in suburban Everett. She said Wright will face federal charges and is expected to appear in U.S. District Court on Wednesday.

DiIorio-Sterling wouldn’t specify the charges, but confirmed they’re related to the Rahim investigation.

Authorities also searched a home in Warwick, Rhode Island, but would not confirm that was linked to the Boston shooting.

Evans said authorities had been watching Rahim "for quite a time," but "a level of alarm" prompted them to try to question him Tuesday.

He said authorities knew Rahim "had some extremism as far as his views," but he would not confirm media reports that Rahim had been radicalized by online propaganda by the Islamic State group.

Evans said the officers didn’t have their guns drawn when they approached Rahim. He said the video shows Rahim "coming at officers" while they were backing away.

That account differs from one given by Rahim’s brother Ibrahim Rahim, who said in a Facebook posting that his youngest brother was killed while waiting at a bus stop to go to his job.

"He was confronted by three Boston Police officers and subsequently shot in the back three times," he wrote. "He was on his cellphone with my dear father during the confrontation needing a witness."

Ibrahim Rahim, a former assistant imam at a Boston mosque, could not immediately be reached for more comment Tuesday. In an email, he said he was traveling to Boston to bury his brother.

The Suffolk district attorney’s office and the FBI said they will investigate Rahim’s shooting, a routine procedure for shootings involving police.

The Council of American-Islamic Relations will monitor the investigation, spokesman Ibrahim Hooper said.

"We have a number of questions," Hooper said. "Why exactly was he being followed? What was the probable cause for this particular stop? Were there any video cameras or body cameras of the incident? How do you reconcile the two versions of the story, the family version being that he was on his normal commute to work at a bus stop?"

Boston voter registration records for Usaama Rahim list him as a student. Records indicate that as recently as two years ago he was licensed as a security officer in Miami but don’t specify in what capacity.

Yusufi Vali, executive director of the Islamic Society of Boston Cultural Center, said the center’s security firm hired Rahim as a security guard for a month in mid-2013. Vali said Rahim did not regularly pray at the center and did not volunteer there or serve in any leadership positions.

Vincent Lisi, special agent in charge of the Boston FBI office, said authorities "don’t think there’s any concern for public safety out there right now."