Reynaldo Rodriguez was 19 with a young son, a good job and no criminal record when he shot and killed a man. As part of an ongoing family feud, someone — Rodriguez believed it was a man named Robert Cuellar — had shot at Rodriguez’s mother and brother. Then Cuellar slapped Rodriguez’s sister.

“I just blew a fuse,” Rodriguez says now of killing Cuellar.

In 1977 he pleaded guilty to second-degree murder, and the judge gave him a choice: A sentence of 15 to 30 years would probably mean parole in 12. A life sentence would make him parole-eligible in 10 years.

Rodriguez chose life. At his sentencing, Saginaw County (Mich.) Judge Gary McDonald made it clear that this was “not the mandatory natural life imprisonment sentence” and said that if Rodriguez was a “model prisoner,” McDonald would recommend release in 10 years.

Thirty-seven years later, Rodriguez is still behind bars.

America’s prisons hold tens of thousands of people like Rodriguez — people primarily confined not by the verdicts of a judge or a jury but by the inaction of a parole board. Michigan is one of 26 states where parole boards are vested with almost unlimited power to decide who gets out of prison when, and why.

With more than 1.5 million people behind bars, the United States has the highest incarceration rate in the world, and the financial costs are staggering. As politicians from both parties seek alternatives to mass imprisonment, the parole process has emerged as a major obstacle.

A months-long Marshall Project investigation reveals that, in many states, parole boards are so deeply cautious about releasing prisoners who could come back to haunt them that they release only a small fraction of those eligible — and almost none who have committed violent offenses, even those who pose little danger and whom a judge clearly intended to go free.

A recent revision of the Model Penal Code, an influential document written by legal scholars, declared parole boards “failed institutions.”

“No one has documented an example in contemporary practice, or from any historical era, of a parole-release system that has performed reasonably well in discharging its goals,” a draft of the document says.