He was the commanding officer of Company C, 1st Battalion, 20th Infantry of the 11th Brigade, Americal Division, the unit responsible for the My Lai massacre of 16 March 1968.

[1] He served 12 years in the enlisted ranks (including his time in the National Guard) before being commissioned through Officer Candidate School in 1964.

[3] According to the 1970 investigation by General William R. Peers, Medina:[4] Because Article 4 of the Fourth Geneva Convention excluded South Vietnamese civilians (whose nation was a co-belligerent with the U.S.) from the status of protected persons in interstate wars, Medina could not be prosecuted for violations of international law related to protected persons.

Medina also strongly denied killing any Vietnamese noncombatant at My Lai, with the exception of a young woman whom two soldiers testified that they found hiding in a ditch.

The defense lawyers brought up many incidents during the Vietnam War of Viet Cong suspects and sympathizers faking surrender to use hidden pistols or grenades to harm or kill American military personnel.

Despite his acquittal, the court martial and negative publicity brought Medina's military career to an end.

He later admitted that, during his court martial, he had "not been completely candid to avoid disgracing the military, the United States, his family, and himself.

"[11] After resigning from the Army, Medina went to work at an Enstrom Helicopter Corporation plant owned by F. Lee Bailey in Menominee, Michigan.