Story highlights Brother identifies suspect who was fatally shot as Usaama Rahim

Man under investigation for possible threats against police officers, says police commissioner

Federal agent and Boston officer fired at man, official says

(CNN) A man who waved a large military knife at officers and is believed to have been radicalized by ISIS was shot and killed by police in Boston on Tuesday, according to officials.

The suspect, identified as Usaama Rahim, 26, was under 24-hour surveillance by anti-terrorism authorities, said FBI Special Agent in Charge Vincent B. Lisi.

Later Tuesday, authorities arrested a second man in connection with the case. The U.S. Attorney's Office in Boston identified him as David Wright. He will appear in Boston federal court Wednesday, spokeswoman Christina Sterling said.

"As of right now, we don't think there is any concern for public safety," Lisi said.

Rahim was a subject of a terror investigation involving suspected Islamist extremists, law enforcement sources said.

Read More