Accused Boston Marathon bombers Dzhokhar Tsarnaev and his brother Tamerlan talked multiple times with each other over Skype just two days after allegedly setting off a pair of bombs on Boylston Street and before they allegedly killed an MIT police officer as they sought to flee the area.
New details about the investigation into the Marathon bombings were revealed by an FBI agent testifying on Tuesday during a motion hearing in the obstruction of justice case of Dzhokhar Tsarnaev's friends.
Prosecutors called Special Agent John Walker to the stand in an attempt to prove that questioning Tsarnaev's friends and searching their apartment was done appropriately and with their consent. Some of the testimony serves as a preview of details that could be used in Dzhokhar Tsarnaev's trial.
Walker said that authorities believed the bombs were detonated remotely and that agents were concerned with the use of cellphones by the Tsarnaev brothers.
"We were very concerned with regard to phones," Walker said, adding that the FBI will soon finish a report on how the bombs were constructed and operated. "We suspected that phones were used in the general commission of the act of terrorism on [Marathon] Monday."
Walker did not say specifically how exactly the Tsarnaev brothers allegedly used the phones on Marathon Monday.
The Tsarnaev brothers are accused of setting off a pair of pressure cooker bombs at the Marathon finish line, killing three people and injuring more than 260 others before allegedly killing an MIT police officer and getting involved in a shootout with police in Watertown days later. Tamerlan Tsarnaev was killed in the shootout. His brother was found hours later hiding in a dry-docked boat.
Walker said that Dzhokhar Tsarnaev subscribed to a cell phone family plan that included four phones.
During the April 19, 2013 manhunt for the younger Tsarnaev, authorities were tracking multiple cell phone tower pings associated with the phones, causing a massive response to New Bedford and eventually the apartment where Tsarnaev's friends, Dias Kadyrbayev and Azamat Tazhayakov lived.
Walker said he received information that a message had been sent to Tsarnaev's parents in Chechnya from a phone connected to Tamerlan Tsarnaev. Walker said that phone use on Friday morning, hours after Tamerlan Tsarnaev was killed in the shootout, pinged off of a tower in New Bedford. He did not offer more details about the message or exactly who may have sent it.
Testimony and cross-examination were expected to continue Wednesday.
On April 19, 2013, authorities raided a New Bedford apartment where Dzhokhar Tsarnaev's friends, Kadyrbayev and Tazhayakov, lived. Authorities received information, including cell phone tower pings, that Tsarnaev could be there.
Walker said the FBI director made the decision to perform a warrantless search of the apartment.
He then talked about questioning the two friends, as well as Kadyrbayev's girlfriend.
"I told them 'Dzhokhar Tsarnaev, effectively he's dead. Whether he's still living or is going to go away, his life is over. Your life is not over,'" Walker said.
Follow Michael Naughton on Twitter @metrobosmike.