Another reason for using a lethal injection is to complete a process of execution for capital punishment when someone has been sentenced by a court of law with a death penalty.
On May 15, 2015; a U.S. jury Sentenced Boston bomber Dzhokhar Tsarnaev to death by lethal injection.
Three people were killed and 260 were injured when Tsarnaev and his brother placed bombs at the finishing line of the Boston Marathon in 2013.
The convicted Boston bomber is likely to be moved to a federal prison in Terre Haute, Indiana, to await execution.
Massachusetts ended the death penalty in 1984, but Tsarnaev was tried on federal charges and so it is possible that he will be legally executed.