Sean Ellis has spent more than half his life behind bars for a murder he insists he did not commit.  He was convicted in 1995 for fatally shooting Boston detective John Mulligan.  On Tuesday, a Superior Court Judge granted Ellis a new trial—his fourth in so many years.  

Defense attorney Rosemary Scapicchio finally succeeded last fall in securing a hearing for her client, 40-year-old Sean Ellis—who for 21 years has maintained his innocence.  The result was Tuesday’s surprise decision by Judge Carol Ball to grant Ellis a new trial.  While Suffolk District Attorney Dan Conley says he strongly disagrees with the decision to vacate the jury’s verdict, he hasn't yet decided to refile charges. If he does, it will reopen a dark chapter involving three Boston detectives: Kenneth Acerra, Walter Robinson, and  John Mulligan.

Mulligan had a tough reputation around town. He was cited by the department as a “problem officer” in a Boston Globe expose.  Still, police were shocked that someone would shoot a cop; not once but five times in the face as he slept in his SUV while on a paid detail in Roslindale on September 26, 1993.

An eyewitness, Rosa Sanchez, identified 18-year-old Terry Patterson of Hyde Park, and 19-year-old Sean Ellis of Dorchester as the men seen hovering near Mulligan's car.  Both men were convicted in 1995 after a third trial – with evidence collected by Detective Kenneth Acera and his partner, Walter Robinson. What the jury did not know was that Detectives Acera and Robinson had been robbing drug dealers for over a decade… with Mulligan allegedly  in on the action from time to time.

Acera and Robinson were themselves convicted of perjury and armed robbery in 1998. Boston police were on to the three detectives as early as 1991, but the Anti-Corruption Unit files were kept hidden – until this August. Those files became the basis for defense attorney Rosemary Scapicchio’s request for a new trial.

Rosa Sanchez was the prosecution’s key witness and Scapicchio argued that her identification of Ellis  effectively stopped the investigation in its tracks, drawing attention away from the corrupt cops, including Mulligan—accused  of falsifying warrants to gain entry into apartments and robbing drug dealers

Curiously, Rosa Sanchez knew Detective Acerra. Her aunt had been romantically involved with him. And Rosa Sanchez initially identified another man as the individual she spotted hanging out near Mulligan's SUV. But Boston Police Detective Daniel Keeler, who worked the original murder investigation, said he had no doubt that Ellis was guilty and told Judge Carol Ball as much during the hearing for a new trial. His comments did not go down well in Suffolk Court with  Rosemary Scapicchio

On Tuesday night as cars whizzed by outside, Sean Ellis was inside MCI-Norfolk meeting with his attorney.  Scapicchio said that Ellis wept when told that that he had been granted a new trial.  That he was given another chance to try to prove his innocence that he’s maintained for 21 years.

**This report was produced in cooperation with the Schuster Institute for Investigative Journalism at Brandeis.

Correction:  An earlier version of this report stated that Ellis and a co-defendant had been identified as the shooters.  They were actually named as the individuals hanging near Mulligan's rented SUV.