Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Officials take crime scene photos a day after two explosions hit the Boston Marathon. Photo: REUTERS/Jessica Rinaldi
Officials take crime scene photos a day after two explosions hit the Boston Marathon. Photo: REUTERS/Jessica Rinaldi
Two men in hazardous materials suits put numbers on the shattered glass and debris as they investigate the scene at the first bombing on Boylston Street in Boston. Photo: AP/Elise Amendola
Two men in hazardous materials suits put numbers on the shattered glass and debris as they investigate the scene at the first bombing on Boylston Street in Boston. Photo: AP/Elise Amendola
Investigators survey the site of a bomb blast on Boylston Street a day after two explosions hit the Boston Marathon. Photo: AP
Investigators survey the site of a bomb blast on Boylston Street a day after two explosions hit the Boston Marathon. Photo: AP
This image from a FBI and Department of Homeland Security joint bulletin shows the remains of a black backpack that the FBI says contained one of the bombs that exploded during the Boston Marathon. Photo: AP/FBI
This image from a FBI and Department of Homeland Security joint bulletin shows the remains of a black backpack that the FBI says contained one of the bombs that exploded during the Boston Marathon. Photo: AP/FBI
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters
Boston Marathon bomb scene pictures taken by investigators show the remains of an explosive device. Photo: Reuters

The bombs that exploded at the Boston Marathon were likely heavy, carried to the scene in dark nylon bags, and fashioned out of pressure cookers packed with shrapnel to make them more lethal, authorities said.

Bomb scene pictures taken by investigators and released on Tuesday show the remains of an explosive device including twisted pieces of a metal container, wires, a battery and what appears to be a small circuit board. - Reuters