Evidence recovered from the scene of the deadly blast in Boston Monday is being investigated by authorities.

Photos show the remains of an explosive device that include twisted metal containers, wires and a battery in what appears to be a small circuit board.

Officials say the evidence is being reconstructed at an FBI lab in Virginia.

FBI SPECIAL AGENT RICHARD "RICK" DESLAURIERS, SAYING:

"Among items partially recovered are pieces of black nylon which could be from a backpack and what appear to be fragments of BBs and nails possibly contained in a pressure cooker."

Authorities say the investigation is still in its infancy and that there are no claims of responsibility.

Three people were killed in the twin blasts, 176 others were injured.