30 April 2015 :

the US Department of Justice confirmed that federal executions have been halted until a review of the federal protocol used by the Bureau of Prisons was completed.
“The Department of Justice has been conducting a review of the federal protocol used by the Bureau of Prisons, and has had a moratorium in place on federal executions in the meantime,” said Justice Department spokesperson Patrick Rodenbush.
The result of the Justice Department’s internal review could impact the sentence of Boston Marathon bomber Dzhokhar Tsarnaev if the jury in the capital punishment sentencing trial returns a death penalty verdict. It is unclear when the DOJ review might conclude, or what actions the agency may take as a result of its findings.