JIMMY GOLEN,Associated Press

BOSTON (AP) — Massachusetts Gov. Deval Patrick says no unexploded bombs were found at the Boston Marathon. He says the only explosives were the ones that went off Monday.

Three people were killed, including an 8-year-old boy, and more than 150 injured by two explosions just seconds apart near the finish line.

Special Agent in Charge Richard DesLauriers says at a news conference there are no known additional threats.

Police commissioner Ed Davis says it is the most complex crime scene in history of the department.

Authorities are looking for amateur video and photographic evidence that can give clues to who set off the bombs.

Suffolk County District Attorney Daniel Conley says "what occurred in Boston was an act of cowardice."