BOSTON -- A prominent anti-death penalty lawyer who has managed to get life sentences for several high-profile clients, including the Unabomber, has joined the defence team representing the Boston Marathon bombing suspect.

Dzhokhar Tsarnaev has been charged with using a weapon of mass destruction during the April 15 marathon. Three people were killed and more than 260 injured when two bombs exploded near the finish line.

A judge on Monday approved the appointment of death penalty expert Judy Clarke to defend 19-year-old Tsarnaev. But judge Marianne Bowler denied, at least for now, a request from Tsarnaev's public defender, Miriam Conrad, to appoint a second death penalty lawyer -- David Bruck, a professor at Washington and Lee University School of Law.

Tsarnaev's lawyers could renew their motion to appoint another death penalty expert if he is indicted, the judge said.

Clarke's clients have included the Unabomber, Ted Kaczynski; Susan Smith, a woman who famously drowned her two children; Atlanta Olympics bomber Eric Rudolph; and most recently Jared Loughner, who shot former Rep. Gabrielle Giffords in the head. All received life sentences instead of the death penalty.

Clarke has rarely spoken publicly about her work and did not return a call seeking comment Monday. However, at a speech Friday at a legal conference in Los Angeles, she talked about how she had been "sucked into the black hole, the vortex" of death penalty cases 18 years ago when she represented Smith.

"I got a dose of understanding human behaviour, and I learned what the death penalty does to us," she said. "I don't think it's a secret that I oppose the death penalty."

Bruck has directed Washington and Lee's death penalty defence clinic, the Virginia Capital Case Clearinghouse, since 2004.

In other developments in the Boston case:

-- FBI agents visited the home of the in-laws of the suspect's brother, Tamerlan Tsarnaev, and carried away several bags. The brother was killed in a gun battle with police.

CNN reported at least one bag was labeled DNA samples.

FBI spokesman Jason Pack confirmed agents went to the North Kingstown home of Katherine Russell's parents Monday. Russell is Tsarnaev's widow and has been staying there.

Russell didn't speak as she left her attorneys' office in Providence. Attorney Amato DeLuca says she's doing everything she can to assist with the investigation.

-- President Barack Obama and Russian President Vladimir Putin discussed terrorism co-ordination Monday in the wake of the Boston Marathon bombings. Obama expressed his "appreciation" for Russia's close co-operation after the attack.

The suspected bombers are Russian natives who immigrated to the Boston area. Russian authorities told U.S. officials before the bombings they had concerns about the family, but only revealed details of wiretapped conversations since the attack.