A U.S. Army Green Beret has been charged with murder for allegedly shooting a man he described as a terrorist suspect while serving in Afghanistan in 2010.

Major Matthew Golsteyn learned Thursday morning that he was being charged with "premeditated murder, a death penalty offense," his attorney Philip Stackhouse tweeted, according to ABC News.

Golsteyn, who has been investigated by the military since 2011, has said the man he shot was a bomb-maker working for the Taliban. He maintains that he did not violate rules of engagement in the shooting death.

In 2011, Golsteyn took a polygraph test while applying for a job with the CIA. He told interviewers that while on deployment in 2010 he and another soldier took the alleged Taliban suspect off-base, shot him and buried his remains, according to NBC News.

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His telling sparked the first investigation, which brought no charges due to a lack of evidence.

Golsteyn later spoke to Fox News in 2016 for a special report called "How We Fight" where he explained how he killed the suspected bomb-maker. The interview sparked another investigation.

Golsteyn’s lawyer told the BBC he would “relentlessly” defend his client against the charges.

"Major Golsteyn is a humble servant-leader who saved countless lives, both American and Afghan, and has been recognised repeatedly for his valorous actions," Stackhouse said.

Golsteyn was a captain when deployed in Afghanistan and his service won him a Silver Star, the third-highest award for valor, when he helped track down a sniper targeting his troops and assisted a wounded Afghan soldier.

The award was later upgraded to the Distinguished Service Cross, the second-highest award for valor, according to the Army Times.

He was stripped of his awards in 2014 as the result of an investigation, though no formal charges were brought against him at the time.