The brothers finished building the bombs in Tamerlan’s apartment in Cambridge, Mass., faster than they anticipated, and so decided to accelerate their attack to the Boston Marathon on April 15, Patriots’ Day in Massachusetts, from July, according to the account that Dzhokhar provided authorities. They picked the finish line of the marathon after driving around the Boston area looking for alternative sites, according to this account.
The new details about what Mr. Tsarnaev has told the authorities emerged as the F.B.I. moved forward on Thursday with trying to determine how the brothers were radicalized and the role that Tamerlan’s wife might have played in the plot or in helping the brothers evade the authorities after the attacks.
As part of those efforts, the authorities have sought to determine whether fingerprints and DNA found on bomb fragments were from Mr. Tsarnaev’s wife, Katherine Russell. According to two other law enforcement officials, Ms. Russell’s fingerprints and DNA do not match those found on the fragments.
Federal authorities are skeptical of Ms. Russell’s insistence that she played no role in the attack or in helping the brothers elude the authorities after the F.B.I. released photos of them. That skepticism has been stoked by Ms. Russell’s decision in recent days to stop cooperating with the authorities.
The F.B.I. has also decided to send more agents to Russia to assist with the investigation, according to one law enforcement official. The bureau has been relying on a couple of agents it has based in the United States Embassy in Russia to serve as an intermediary with the authorities there. (More)