The US attorney general, Eric Holder, has authorised prosecutors to seek the death penalty for Boston Marathon bombing suspect Dzhokhar Tsarnaev, the Justice Department has announced.

A trial date has not yet been set for Tsarnaev, 20, who was indicted in June on 30 federal counts, including 17 that carry the death penalty.

Prosecutors say Tsarnaev and his brother, Tamerlan Tsarnaev, placed two bombs near the end of the marathon on 15 April 2013. Three people were killed and more than 260 injured in the attack. Tsarnaev is also accused of participating in the murder of a police officer at the Massachusetts Institute of Technology. Tamerlan Tsarnaev, 26, died in a confrontation with police after the bombing.

Fifty-seven per cent of Boston residents want a sentence of life without parole for Tsarnaev, compared with 33% who would like to see him receive the death penalty, according to a Boston Globe poll conducted in September.

Three prisoners have been executed under the federal death penalty since it was reinstated in 1988, and another 59 are on federal death row, according to the Death Penalty Information Center. Many more have been executed under state death penalty laws. Massachusetts has a state ban on the death penalty, however, that does not apply to Tsarnaev because he is being tried federally.

If Tsarnaev is found guilty, a jury would have to reach unanimous agreement in order for a death sentence to be imposed.

