Boston: Images show two possible suspects

Investigators pinpointed two possible suspects in the Boston Marathon bombing after they appeared in images near the finish line moments before the blasts, a law enforcement official said.

The twin blasts killed three and injured about 180 others Monday, sending shock waves nationwide. They left behind gruesome images of mayhem, destruction and shattered limbs.A President Barack Obama and first lady Michelle Obama are scheduled to attend an interfaith service for the victims in Boston on Thursday morning.And as the city prepares to pay tribute to the victims, details are trickling in about the tragic day.

In the images, one of the men is seen carrying a black backpack. An FBI official has said that the bombs were placed inside a black nylon backpack or bag. Authorities did not name the two � both men � but their photographs have been distributed to law enforcement, the official said. The photos will not be released to the public for fear of impeding the investigation, according to the official.

Earlier on Wednesday, two sources with knowledge of the investigation identified a man as a possible suspect in the attack, but did not name him. Seen on a video, the man wore a white baseball cap. One of the sources added that the cap was on backward and the man was also wearing a light-coloured hooded sweatshirt and a black jacket. It was not immediately clear if he is one of those alluded to in the photographs distributed to law enforcement officials.

Investigators are closer to cracking the case 'every hour,' Massachusetts Governor Deval Patrick said. He urged patience to allow authorities space to do their job. "I wish they had nailed the perpetrator within minutes of this catastrophe, but I understand from experience it's going to take some time," he said.