The FBI converged on an apartment in the North End of Boston Wednesday.
Investigators were in and out of a small apartment building on Fulton Street all day.
The FBI said it was on the scene in connection with a federal investigation.
In-depth news coverage of the Greater Boston Area.
"I went out to eat, come back, and there's, like, a full-on CSI-type investigation," said Jonny Friedman, who lives in the building.
He says investigators were searching the basement and the third-floor apartment right above his, and asking questions about a tenant named Trevor Lucas.
The United States Attorney's Office confirms Lucas was arrested Wednesday for violating the terms of his release from federal prison.
Investigators with the FBI's Violent Crimes Task Force and Evidence Response Team could be seen removing what's presumed to be evidence in the case that's now under investigation.
The FBI said there's no threat to public safety.
The U.S. Attorney's Office says Lucas was released from federal prison last year following a conviction in Wisconsin for a firearms charge in connection with an attempted kidnapping.