BOSTON (Reuters) - Police investigating the deadly blasts at the Boston Marathon said on Tuesday they had recovered fragments of black nylon that may been from a bag used to conceal one or both of the bombs detonated at the race, the FBI official leading the probe said.
FBI Special Agent in Charge Richard DesLauriers said investigators also had recovered fragments of BBs and nails from the scene of Monday's back-to-back explosions, which killed three people and wounded more than 170 others. The devices may have been constructed from pressure cookers, he said.
Separately, President Barack Obama will come to Boston on Thursday to attend a memorial service for the blast victims, Massachusetts Governor Deval Patrick said.
(Reporting by Scott Malone; Writing by Dan Burns; Editing by Eric Beech)