Evidence photos from Boston bombings

Updated 3:44 PM ET, Wed January 21, 2015
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A police forensics team examines a boat April 22, 2013, in Watertown, Massachusetts, where Boston Marathon bombing suspect Dzhokhar Tsarnaev was discovered several days earlier and taken into custody. Barcroft Media /Landov
Massachusetts State Police released thermal images of Tsarnaev hiding in the boat on April 19, 2013. They were taken by an infrared device on a helicopter. The first image was taken at 7:19 p.m., less than 20 minutes after a homeowner told police there was a bloodied person in his boat. Massachusetts State Police
This image from 7:22 p.m. shows a white heat signature large enough to be a person. Massachusetts State Police
A robotic arm tears away the cover on the boat at 7:36 p.m. Massachusetts State Police
The heat signature clearly shows the suspect's feet and the rest of his body behind the boat console at 8:01 p.m., minutes before he surrendered. Massachusetts State Police
Boston Marathon bomb scene pictures, taken by investigators, show the remains of an explosive device. Reuters/Landov
A federal law enforcement source with firsthand knowledge of the investigation told CNN that a lid to a pressure cooker -- thought to have been used in the bombings -- had been found on a roof of a building near the scene. Reuters/Landov
One bomb was housed in a pressure cooker hidden inside a backpack, the FBI said in a joint intelligence bulletin. Reuters/Landov
The device also had fragments that may have included nails, BBs and ball bearings, the FBI said. Reuters/Landov
The recovered parts include part of a circuit board, which might have been used to detonate a device. Reuters/Landov
A law enforcement official said the bombs were probably detonated by timers. But the FBI said details of the detonating system were unknown. Reuters/Landov
Scraps of at least one pressure cooker, nails and nylon bags were sent to the FBI's national laboratory in Virginia, where technicians will try to reconstruct the devices, the agent leading the investigation said. Reuters/Landov
The U.S. government has warned federal agencies in the past that terrorists could turn pressure cookers into bombs by packing them with explosives and shrapnel and detonating them with blasting caps. Reuters/Landov
The pieces suggest each of the devices was 6 liters (about 1.6 gallons) in volume, a Boston law enforcement source said. Reuters/Landov
"It has the hallmarks of both domestic and international (attacks), and you can see either side of that," former FBI Assistant Director Tom Fuentes told CNN. Reuters/Landov