BOSTON - Investigators were seeking a motive for the Boston Marathon bombings and whether others were involved as they awaited a chance on Sunday to interview the surviving ethnic Chechen suspect.

Dzhokhar Tsarnaev, 19, was in a Boston hospital seriously wounded and unable to speak, after he was captured late on Friday at the end of a huge manhunt that shut down Boston.

His brother, Tamerlan, 26, was killed in a firefight with police earlier on Friday.

Investigators are trying to establish whether others may have had a role in the detonation of bombs made in pressure cookers and packed with ball bearings and nails that exploded at the Boston Marathon on Monday, killing three people and injuring 176.

Tamerlan traveled to Moscow in January 2012 and spent six months in the region, a law enforcement source said. But it was unclear what he did while he was there and if he could have had contact with militant Islamist groups in southern Russia's restive Caucasus region.

Authorities have yet to charge Dzhokhar, who will be defended by the Federal Public Defender Office that represents criminal suspects who cannot afford a lawyer.

Sources had suggested he would face charges on Saturday but late in the evening officials from the US Attorneys' Office and the Department of Justice indicated no statements would be issued before Sunday.

Please LIKE our Facebook page - it makes us stronger