His arrest in 1965, for a heroin sale to an undercover federal agent, produced the imprisonment that would prove to be his last. He entered prison for what he has described as his final sentence, and what happened inside that sentence was the thing that changed the direction of his life.
In 1968, at Soledad Prison in Monterey County, a riot broke out. Trejo threw a rock at a prison guard. The charge that resulted — assault on a correctional officer — carried consequences severe enough, in the context of his prior record, that the outcome of the case was genuinely uncertain and the potential consequences were severe. He has described this period — sitting in solitary confinement, facing a possible extended sentence, confronting the real possibility that the life he had been living was going to consume whatever remained of him — as the turning point.
In solitary, he made what he has described as a prayer, a deal, a commitment: if he survived this, he would try to help other people. The charges were eventually dropped. He was paroled in August 1969.
The charges being dropped does not appear to have been the product of a formal exoneration or a determination that he had not thrown the rock. The documentary record, as available in the biographical sources consulted for this article, indicates that the charges were dropped in the process of his eventual release. The specifics of the legal process are not documented in the sources available here with sufficient detail to characterize precisely.