BOSTON -- Investigators have stepped up their interest in the widow of one of the suspects in the Boston Marathon bombings after finding radical Islamist material on her computer, according to a federal law enforcement source.
The material included Inspire, al-Qaida's online magazine, the source said.
The new focus on Katherine Russell, 24, the widow of Tamerlan Tsarnaev, came as forensic tests detected residue from explosives in the bathtub and kitchen sink in the couple's Cambridge apartment.
The results, according to the source, appear to corroborate the surviving suspect's statements to federal investigators that the brothers built the bombs in the apartment.
Dzhokhar Tsarnaev, 19, had told investigators that he and his older brother learned to make the pressure-cooker bombs detonated at the marathon using instructions from Inspire, which advocates jihad in the name of Islam.
DNA found on a piece of one of the marathon bombs did not match a DNA sample from Russell, the source said.
Phone call in question
Investigators hope to learn more about a phone call Tamerlan Tsarnaev, 26, made to his wife on April 18, three days after the bombings -- and after the FBI first circulated photographs of the suspects. The content of the phone conversation hasn't been disclosed.
Key questions for investigators are what role, if any, Russell played in the plot or its aftermath -- and whether she downloaded the material found on her computer.
Her attorney, Amato DeLuca, has said his client played no role and was shocked to learn of her husband's involvement.
But Russell did not report the phone call to authorities when the massive manhunt was under way, the source said, and she is no longer cooperating with investigators.
Investigators have said the brothers had planned to wait until July 4 to launch an attack but moved the date up and decided to act on April 15 -- Patriots Day in Massachusetts -- because the explosives were ready.
The bombs, set off near the marathon finish line, killed three people and injured more than 260. In the days after the bombings, a Massachusetts Institute of Technology police officer was shot dead and a Massachusetts Bay Transportation Authority officer was wounded by the Tsarnaevs as they tried to escape, authorities said.
Federal, state and local authorities on Friday began searching a wooded area near Dartmouth, Mass. -- close to where Dzhokhar Tsarnaev had attended college -- for evidence of explosives, according to the U.S. attorney's office in Massachusetts.
Federal agents were acting on information that University of Massachusetts-Dartmouth students reported hearing explosions in the wooded area about a month ago, raising the possibility that the area was used as a testing ground for the homemade bombs. Bomb-sniffing dogs will be used in the search, authorities said.
Three of Dzhokhar Tsarnaev's former classmates have been arrested, accused of removing a backpack and laptop from Tsarnaev's dorm room after the bombings in an attempt to help their friend evade arrest.
Dzhokhar Tsarnaev is in federal custody but remains in a hospital recovering from wounds. His brother died after an early morning shootout with police in the suburb of Watertown four days after the bombings.
The death certificate released Friday says Tamerlan Tsarnaev died from gunshot wounds to his "torso and extremities and blunt trauma to head and torso."
The funeral director of a Worcester mortuary confirmed Friday that it will handle the arrangements.
Plans for suspect's funeral
Peter Stefan, of Graham Putnam & Mahoney Funeral Parlors, said his staff collected Tsarnaev's body from a North Attleborough funeral home around midnight Thursday after that facility was "overwhelmed" by news organizations and community protesters.
Stefan said he's not daunted by the task of burying a suspected terrorist. "I can't separate the saints from the sinners. I bury the dead. That's what I took an oath to do, and that's it."
He said he's known in town for burying the indigent and criminals -- even murderers.
"If someone wants to make a law that all dead terrorists and murderers get thrown in the garbage, that's fine, but that's their job," he said. "Right now, I'm just doing mine."
Stefan said Tsarnaev's uncle, Ruslan Tsarni, is handling the arrangements.
The funeral director said he's been told that Dzhokhar Tsarnaev's lawyers are requesting an independent autopsy.
After the possible second autopsy, he said, the body will be repaired, and relatives will arrange for it to be washed by Islamic men as part of a traditional death ritual. The body will be wrapped in a shroud before it's taken to the cemetery for a simple graveside ceremony.
Where Tamerlan Tsarnaev will be buried is the next headache for Stefan. Cemeteries in Massachusetts and New Jersey have refused to accept the body, and the logistics of getting it to Tsarnaev's family in Russia proved insurmountable, he said.
With Zachary R. Dowdy