Though the United States has the world’s largest prison population, attempts to roll back mass incarceration have largely been limited to inmates convicted of nonviolent crimes. Though more than half of those in state prisons were convicted of hurting or killing someone, their release has been, politically, off limits. Now an effort has begun in Ohio to change that, one case at a time.

Mr. Robinson, 42, the man who killed Veronica Jackson, has spent over half of his life and all of the 21st century locked away. He has stayed out of trouble, earned his GED, learned how to operate a forklift, picked up the guitar and started teaching himself Spanish. His first chance at parole — a long shot at best — will come in 2026.

Prisoners like him are often left out of campaigns to change the criminal justice system, which tend to use the well-tested message that nonviolent drug offenders do not belong behind bars. Last fall, supporters of a measure in Ohio that would have reduced penalties for drug offenses used just that kind of rationale.

It bothered David Singleton, a professor at Northern Kentucky University’s law school who runs the Ohio Justice and Policy Center. Even as he championed the proposal, he thought of Mr. Robinson, whom he had known for years.

“It felt like we were throwing a whole lot of people under the bus,” Mr. Singleton said.

In 1997, Mr. Robinson, 20 at the time, was among several people who had gathered in an apartment in Cincinnati’s West End to sell drugs, a group that included Veronica Jackson, 34. A gang of men in ski masks suddenly showed up, tried to force open the door and fired shots into the apartment. Ms. Jackson fled to a back bedroom where Mr. Robinson was with the cocaine.