Two photos obtained by NBC station WHDH of Boston show a bag on the curb before one of Monday's explosions. The bag wasn't there after the blast. These are among the thousands of photos the FBI is investigating.
The FBI is examining thousands of photos from before and after Monday's deadly bombings at the Boston Marathon to determine whether nylon bags might have been placed in trash bags to appear less conspicuous.
Investigators believe the explosives used Monday were pressure cookers placed in nylon bags. The blasts killed three people and injured at least 176 others.
Among the photos under review are the two above, which were given to NBC station WHDH of Boston by a witness.
Several officials have told NBC News that the WHDH pictures show the point where the blast occurred.
The first picture shows a bag next to a mailbox along a barricade on the marathon route. The second — which the station said it had blurred because of its graphic nature — appears to show no sign of the bag. It is not known what the bag contained.
The person who took the pictures told WHDH that as long as an hour may have passed between the times the two photos were taken.
Boston Police Commissioner Ed Davis said investigators were looking at thousands of photos and wanted as many as the public could send in to firstname.lastname@example.org.
Jim Cavanaugh, a former special agent for the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, said the experts know what to look for.
"They're able to recognize the minute pieces of an article that a civilian wouldn't even know ... but to a bomb investigator, like ATF or FBI, will say, 'That's from a clock; that's from a battery,'" Cavanaugh told NBC News
NBC's Pete Williams discusses two images taken before and after the Boston bombing that are generating a lot of interest. The first shows a bag next to a mailbox along a barricade on the marathon route. The second appears to show no sign of the bag.
This story was originally published on Tue Apr 16, 2013 8:48 PM EDT