Zachary Gibian was convicted in 2006 of nearly beheading retired police officer Scott Nager in his home in Hauppauge, on Long Island. Gibian was 20 at the time. He's serving 25 years to life in prison.
The Appellate Division of the state Supreme Court ruled errors were made in his trial. It faulted the trial judge for not allowing testimony about statements supposedly made by Gibian's mother.
Gibian testified it was his mother who killed Nager after she discovered her husband sexually abusing her son. She denied the allegations.
Prosecutors say they'll appeal the latest ruling.
