Accused Boston bomber's lawyers challenge jury-selection process

"Extra precautions must be taken to protect the defendant's right to an impartial and representative jury in a capital case," his attorneys argued in a motion filed in US District Court in Boston.

Defense lawyers have asked US District Judge George O'Toole three times to move the trial out of Boston, contending that it would be impossible to seat an impartial jury in the city where so many residents were either present at the race or ordered to shelter in their homes four days after the attack as police searched for Tsarnaev.

The judge rejected all three requests, and attorneys are now waiting for an appellate panel to rule on the matter.

Tsarnaev, an ethnic Chechen who moved to the United States with his family a decade before the attack, is also charged with shooting dead a university police officer on April 18, 2013, as he and his older brother, Tamerlan, tried to flee the city.

Tamerlan died that night following a gunbattle with police.