In a nine-page document seen by AFP, one of Tsarnaev's lawyers, Judy Clarke, sought the recruitment of Virginia-based lawyer David Bruck citing the "extraordinary nature" of the case.

Tsarnaev, 19, faces a 30-count indictment -- including 17 counts punishable by death -- for his role in the April attacks in Boston which left three people dead and more than 260 injured.

"Even were this not a potentially capital case, the magnitude of the task confronting Mr Tsarnaev's attorneys would be daunting," Clarke wrote, noting Bruck had specialized in death penalty cases for 33 years and was one of the most "well-regarded" attorneys in the United States.

Bruck is best known for representing Said Safarini, one of the hijackers of a 1986 Panam flight. The Jordanian was sentenced to 160 years in prison in May 2004.

He also represented Al-Qaeda bomber Mohamed Rashed Al Owhali, sentenced to life in prison in 2001 for his role in the 1998 attacks on US embassies in East Africa.

Clarke also specializes in high-profile death penalty cases, most notably defending "Unabomber" Ted Kaczynski, serving life in prison without possibility of parole for a wave of bombings which left three people dead. (AFP)