Judith Clark, who drove a getaway car in the infamous 1981 robbery of a Brink’s armored car in Rockland County, N.Y., that left a guard and two police officers dead, went into prison defiant, with seemingly little chance of getting out. The judge who sentenced her saw her as beyond rehabilitation, giving her a minimum of 75 years in prison and all but ensuring she would die there.

But Gov. Andrew M. Cuomo, citing what he called Ms. Clark’s long sentence and “exceptional strides in self-development” commuted her sentence on Friday.

Mr. Cuomo’s action does not undo Ms. Clark’s conviction on second-degree murder and robbery charges, but it reduces her sentence to 35 years to life and makes her eligible for parole in 2017.

If Ms. Clark is freed, it would be in recognition of her evolution from radical to model prisoner, and serve as a coda to a notorious case that was among the last gasps of violent left-wing extremism seen in the 1960s and 1970s.