More than ten square blocks are still locked down in the heart of the Boston this afternoon as investigators continue to sift through debris, searching for answers in the wake of the twin blasts that killed at least three people and wounded more than 140 others.
"This is the most complex crime scene in history of department," said Boston Police Commissioner Edward Davis.
For now, investigators won't discuss specifics about the explosive devices that triggered two violent blasts killing three people.
Among the dead was 8-year-old Martin Richard, who died just after seeing his dad cross the finish line.
The search for suspects led to a suburban apartment in Revere, Massachusetts overnight where investigators removed bags of potential evidence.
Agents won't discuss what they found and say there is no suspect in custody.
Doctors continue to work around the clock as well more than 100 victims are still in area hospitals, many with wounds from shrapnel doctors say was added to the devices to maximize the carnage.
"This bomb had multiple metallic fragments in them and we removed pellets and nails," said Dr. George Velhamos.
One of several factors pushing investigators to find the person or people responsible.