He is notable for alleged involvement in war crimes alongside 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 by a sniper 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.
He would later be named in 7 of the 30 allegations that the Army would later investigate the unit for, including the rape and fatal stabbing of a 13-year-old girl and the killing of a 15-year-old boy.
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.