Two explosives went off near the finish line at the Boston Marathon Monday afternoon.
Investigators said they believe it was two small home-made bombs that did the damage, which killed three people, including an eight-year-old boy, and injured more than 130 others just before 3 p.m.
Officials said, as of Monday night, there is still no suspect.
Boston police said they would continue working to find those responsible.
F.B.I. reps called it a "potential terrorist investigation". Massachusetts Governor Deval Patrick (D), asked citizens to be on a heightened state of alert during a press conference the same day.
Anyone with information, pictures, or video pertaining to the bomb blasts are asked to contact Boston Police at 800-494-8477.