BOSTON – The search for forensic evidence turned up pieces of black nylon that could have been from a bag or backpack at both blast sites, DesLauriers said. Law enforcement sifting through the damage also recovered pieces of BBs and nails, possibly from a pressure-cooker explosive device used to maximize injuries.

No group or individual has claimed responsibility for the attack, which killed at least three people and wounded more than 180 others.

“Someone knows who did this,” DesLauriers said. “The person who did this was someone’s friend, neighbor or co-worker.”

The podium for Tuesday evening’s press conference at the Westin Hotel was filled with officials, including Massachusetts Gov. Deval Patrick; Boston Mayor Tom Menino, recovering from leg surgery and seated in a wheelchair; Police Commissioner Ed Davis; and others drawn from the vast ranks of the law enforcement agencies involved in the case.

Patrick urged observers and Boston residents to refrain from racial profiling as the investigation continues.

“There are times when all kinds of forces conspire to make people think of categories of people sometimes in uncharitable ways,” he said, adding that no such incidents stemming from the attacks have been reported. “We are one community and we are all in this together.”  (read more)