Mueller plowed through officer candidate school at Marine Corps Base Quantico, Army Ranger School, and Army jump school before he was shipped out to Vietnam, according to Time. Commander of a rifle platoon of the 3rd Marine Division, he was a recipient of the Bronze Star with Valor, two Navy Commendation Medals, the Purple Heart, and the Vietnamese Cross of Gallantry, according to his FBI bio.

His citation for the Bronze Star with Valor, his first decoration earned just weeks after arriving in Vietnam in December 1968 after his platoon came under heavy fire in the Quang Tri Province, lauded Mueller’s “courage, aggressive initiative, and unwavering devotion to duty.”

“Second Lieutenant Mueller fearlessly moved from one position to another,” the citation reads, according to Graff. “With complete disregard for his own safety, he then skillfully supervised the evacuation of casualties from the hazardous area and, on one occasion, personally led a fire team across the fire-swept area terrain to recover a mortally wounded Marine who had fallen in a position forward on the friendly lines.

That same devotion to duty would serve Mueller just four months later in April 1969, when, as a second lieutenant, he led his platoon to rescue American troops pinned down under heavy fire from the Vietcong. Despite taking an AK-47 round through the thigh, Mueller held his position until the troops had safely retreated. The firefight earned him a Navy Commendation Medal and his Purple Heart; a month later, he was back on patrol in the jungles of Vietnam (“I thought I’d at least get to go to a hospital ship,” he reportedly quipped of his injuries.)