BOSTON -- The FBI is working with local and state police to determine if there is a link between a recent rash of bomb scares and bank robberies.

The most recent bomb threat came Friday morning when a suspicious device was found on the front steps of the Lawrence courthouse.

Officers said workers at the Lawrence District Court at 2 Appleton St. were asked to leave about 7 a.m. after a suitcase was found outside with a cell phone on it with a note attached to the phone.

"It was a light brown briefcase and there was a cell phone taped on it with a note," courthouse maintenance worker Norman Eldredge said. "I don't touch it. I peeked down and (the note) just said, 'Notify all news agencies and call the state police.'"

The suitcase and phone were discovered on a walkway overhang. It was safely detonated at 10:30 a.m.

In the past week, police have been called to investigate suspicious devices in Holbrook, Needham and Wellesley. In two of those incidents, banks were robbed nearby while police were occupied investigating the devices.

"At 7 o'clock, we had sufficient time to ensure that every bank and credit union in the city was covered in the event that there was some connection with the two previous incidents," Lawrence Police Chief John Romero said.

Authorities said they were looking into whether any of the previous incidents were related.