GBH News has learned that Boston attorney Rosemary Scapicchio is filing for a new trial for Sean Ellis to clear her client of a gun conviction that remains even after his conviction in the 1993 murder of Boston Police detective was overturned after he spent more than 22 years in jail.

Detective John Mulligan was murdered during the early morning hours Sept. 26, 1993 while sitting in his car outside a Walgreens store in Roslindale, off American Legion Highway.

Ellis and a co-defendant, Terry Patterson, who was tried separately, were tied to the murder based on evidence produced by detectives who themselves were under investigation at the time for corruption. That information was never relayed to the defense and Ellis was ordered released from prison in 2015 by a Suffolk County judge who concluded that Ellis had not received a fair trial. But the conviction on illegal possession of the murder weapon was left in place.

Three years later, former Suffolk County DA John Pappas declined to retry the murder case fearing that the prosecution could not win a conviction. But Pappas and Boston Police Commissioner William Gross continue to insist on Ellis’s guilt.

Mulligan was shot five times in the face with a .25-caliber pistol. Scapicchio says her client had nothing to do with the murder or the gun and will be going to court in the coming days to prove it. For 22 years and 7 months that he was behind bars Ellis maintained his innocence and says that a jury trial may be the only way to demonstrate that conclusively.

The Sean Ellis case is the subject of a new Netflix docuseries called Trial 4.