Boston bomber faces death sentence as jury starts deliberations

US jurors have begun deliberations in the trial of Boston bomber Dzhokhar Tsarnaev, tasked with determining whether he is guilty on 30 counts over the deadly 2013 attacks.

Three people were killed and 264 others wounded in the twin blasts at the city's marathon, the worst attack in the United States since the September 11, 2001 attacks on New York, Washington and Pennsylvania.

Government prosecutors portrayed the Muslim immigrant, who became a US citizen in 2012, as a callous terrorist who carried out the bombings to bring holy war to the northeastern US city and punish the United States.

Tsarnaev's lawyers admit that he planted one of the bombs in the April 15, 2013 attacks, but have portrayed him as a feckless accomplice, bullied or manipulated into taking part by his more radical elder brother.

The defendant looked pale and drawn in court Tuesday as federal judge George O'Toole sent the 12-member jury to commence deliberations.

The seven women and five men are armed with lengthy instructions on how to determine whether Tsarnaev is guilty on each count over the attacks, the murder of a police officer, a car jacking and a shootout while on the run.

Seventeen of those charges carry the possibility of the death penalty.

Deliberations cap the end of the first stage of the one-month trial at the US district court in Boston.

If Tsarnaev is convicted, the trial will enter a second stage, when the jury determines whether he should be executed or spend the rest of his life behind bars without parole -- the only sentencing options available.