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Ybarra was born and raised on the San Carlos Apache Indian Reservation in Arizona to a Mexican father and an Apache mother. When he was five, his father died in a bar brawl, and after that he was raised by his mother. He attended Globe High School in Globe, Arizona, and was arrested four times as a teenager for disturbing the peace and underage drinking.
Ybarra enlisted in the U.S. Army in 1966, along with his childhood friend Kenneth Green, and the friends were attached to the Tiger Force unit. Both he and Green committed atrocities against Vietnamese civilians during the war, and engaged in the Tiger Force practice of cutting off trophy ears from their victims.
Green was killed on September 29, 1967, and other Tiger Force soldiers claim that it threw Ybarra over the edge, as he vowed to avenge his friend's death. As a result, he became the unit's worst killer, and had to be transferred out of the unit to an artillery company in early 1968. Ybarra went on to be court martialed for insubordination, and was dishonorably discharged in late 1968. He would later be named in 7 of the 30 allegations that the Army would later investigate the unit for.
Once discharged, Ybarra could not be compelled to testify to the investigations against him, and declined three times. He died of pneumonia in 1982, at age 37, living with his mother on the San Carlos Apache Reservation in Arizona, reportedly contrite and depressed over his role in the war.