The court today reversed the conviction of Richard Anthony Gonnella for the 2002 shooting death of John Henry Williams.
Evidence showed that Gonnella and Christopher Evans went to Williams' apartment. Evans said he heard a gunshot while waiting in his car.
The two later turned themselves in, and Evans told police where to find the gun.
Gonnella was convicted of felony murder and sentenced to life in prison.
Evans was sentenced to 15 years after a guilty plea to voluntary manslaughter.
The court said prosecutors deprived Gonnella of the ability to impeach Evans' testimony.