Boston bomber sentenced to death - is there still a justification for using the death penalty?

A jury in the US has decided that the man who helped carry out the Boston marathon bombing should be sentenced to death. Three people were killed and more than two hundred and sixty others were injured when Dzhokhar Tsarnaev (Jo-kar Tsar-nay-ev) left home-made bombs at the finishing line in 2013. His brother, who was also involved, was shot dead by the police.