The Pentagon has announced it will execute a former US Army major by firing squad, the first such military execution in more than 60 years.
Nidal Malik Hasan fatally shot 13 unarmed US soldiers at Fort Hood in 2009, injuring another 32.
Pentagon spokesperson Sean Parnell announced on social media on Monday that Secretary of War Pete Hegseth had made the recommendation and President Donald Trump approved it.
It will be the first military execution by firing squad since the end of World War Two.
Parnell said the secretary of the Army will set the time and place of the execution.
"Judgement day for Hasan has finally come," he wrote on X.
Hasan, a US Army psychiatrist from Virginia, killed 13 soldiers at the base in Texas in 2009 and later admitted in court he was the gunman and apologised for "any mistakes".
He said during his court-martial in 2013 that he believed he was protecting Muslims and the Taliban in Afghanistan.
The killings on 5 November 2009 were the deadliest ever non-combat attack on an American military base.
The attack took place in a crowded medical building where deploying soldiers were awaiting check-ups and vaccines.
Hasan is currently one of four inmates on the US military's death row.
A military execution requires approval from the US president, according to military law.
It also requires appellate review and a final judgment on its legality to move forward.
The US Court of Appeals for the Armed Forces deemed the military death penalty unconstitutional in 1983 but it was reinstated the following year by an executive order under then-President Ronald Reagan.
Military executions differ from those carried out at the state level.
The majority of executions in the US are carried out on the state level, with 27 states, the military and the federal government still having capital punishment as a legally available option.
Death by firing squad is rather uncommon. There was an execution by firing squad carried out last year in South Carolina, a first for the state and the first time the method was used in the US in 15 years.
Four other states allow the use of a firing squad, including Idaho, Mississippi, Oklahoma and Utah.