President Donald Trump has tweeted that he plans to "review" the case of US soldier Mathew Golsteyn, charged with murdering an Afghan civilian in 2010.
The Army Green Beret Major allegedly shot someone he described as a suspected Taliban bomb-maker during his deployment.
He was charged with murder last week, allegations he denies.
But President Trump has complicated proceedings with his tweet, saying he will now be "reviewing the case".
Maj Golsteyn "could face the death penalty from our own government", he wrote, saying he was getting involved in the case "at the request of many".
At the request of many, I will be reviewing the case of a “U.S. Military hero,” Major Matt Golsteyn, who is charged with murder. He could face the death penalty from our own government after he admitted to killing a Terrorist bomb maker while overseas. @PeteHegseth @FoxNews— Donald J. Trump (@realDonaldTrump) December 16, 2018
It is unclear what the president meant when he posted the tweet.
However, as Commander in Chief of the US armed forces, any intervention by Mr Trump could count as unlawful command influence, and might mean the case against Maj Golsteyn is thrown out.
A Pentagon spokesperson said on Sunday that the allegations against the major are "a law enforcement matter".
"The Department of Defense will respect the integrity of this process and provide updates when appropriate."
What are the charges against Maj Golsteyn?
During his deployment to Afghanistan in 2010, then-Captain Golsteyn allegedly shot a man he described as a suspected Taliban bomb-maker.
He allegedly admitted to the killing as part of a lie detector test taken during a CIA job interview in 2011. This led to an investigation by the Army Criminal Investigation Command.
In April 2014, he got off with an official reprimand because of lack of evidence.
But two years later, Maj Golsteyn spoke on a Fox News special report, titled "How We Fight", about how he killed the suspected bomb-maker.
He told the anchor he shot the man because he was concerned he would kill Afghan informants if released.
What's the latest?
On Friday, Maj Golsteyn was charged with premeditated murder - which carries a possible death penalty.
US Army Special Operations Command spokesman Lt Col Loren Bymer said in a statement: "Major Matthew Golsteyn's immediate commander has determined that sufficient evidence exists to warrant the preferral of charges against him."
Maj Golsteyn's lawyer, Phil Stackhouse, told US media he would be "relentless" in defending his client from the charges, which he was notified of on Thursday.
"Major Golsteyn is a humble servant-leader who saved countless lives, both American and Afghan, and has been recognised repeatedly for his valorous actions," Mr Stackhouse said.
A congressman sided with Maj Golsteyn, writing a letter to the secretary of the US Army to complain about the investigation.
Duncan Hunter, a California Republican, called for an end to the "retaliatory and vindictive" inquiry into "a distinguished and well regarded Green Beret".