The Supreme Judicial Court today affirmed an order for a new trial for Sean Ellis, one of two men convicted of fatally shooting BPD Det. John Mulligan in a Roslindale parking lot in 1993.

The Suffolk County District Attorney's office says it will once again try Ellis for first-degree murder - in what will be his fourth trial on the charge.

The court had rejected Ellis's first appeal for a new trial in 2000, but agreed this time with a Superior Court judge that he should get a new trial because of the discovery of "evidence regarding the victim's participation in crimes of police corruption with several Boston police detectives who investigated his murder, and information provided to the police regarding possible third-party culprits."

A new trial will let Ellis's lawyer make the case her client had nothing to do with Mulligan getting shot in the face five times as he slept in a car outside the Walgreens on American Legion Highway while on an overnight detail.

Instead, attorney Rosemary Scapicchio may get the chance to use FBI and internal BPD documents, some of which prosecutors say they will object to, to argue that Mulligan was one of several corrupt detectives - some of whom played key roles into the investigation that led to the arrest of Ellis and another man - and that plenty of people wanted him dead: Associates of the pot dealer he and other detectives allegedly robbed of $26,000 a few days before his death, another Boston cop whose son, himself a Suffolk County corrections officer, had told a detective wanted to kill Mulligan for not leaving the cop's 14-year-old daughter alone, and the pimps, prostitutes, bar owners, bookmakers, and the owners of second-hand jewelry stores Mulligan allegedly shook down on a regular basis.

The state's highest court said the old and new evidence might make a case that Ellis had someething to do with the killing, but only after the fact, that that is not the same as murder, and that it might have ruled differently in denying Ellis a new trial in 2000 had it known about the evidence.

"We did not know at that time that these detectives had been engaged with the victim in criminal acts of police misconduct as recently as seventeen days before the victim's murder. The complicity of the victim in the detectives' malfeasance fundamentally changes the significance of the detectives' corruption with respect to their investigation of the victim's murder. Without the victim's complicity, the defendant could argue that these detectives had engaged in misconduct with respect to other investigations and therefore might have been more likely to have engaged in misconduct with respect to this investigation. But with the victim's complicity, these detectives would likely fear that a prolonged and comprehensive investigation of the victim's murder would uncover leads that might reveal their own criminal corruption. They, therefore, had a powerful incentive to prevent a prolonged or comprehensive investigation, and to discourage or thwart any investigation of leads that might reveal the victim's corrupt acts."

The court continued:

"We agree that the defendant's possession and concealment of these weapons only days after the killing, combined with the evidence that he was at the Walgreens at or about the time of the killing, is evidence that he was involved in the killing in some fashion. And, had the defendant been charged with being an accessory after the fact to this murder, this evidence would be more than sufficient to support his conviction of that indictment. ... But, as demonstrated in the first trial, where the jury found the defendant guilty of the firearm indictment but were unable to reach a verdict regarding the indictments for murder and armed robbery, his possession and concealment of these firearms does not necessarily mean that he was the shooter or knowingly participated with Patterson in the shooting. ...

"[W]ith this newly discovered evidence, a reasonable jury likely would have had diminished confidence in the integrity and thoroughness of the police investigation in general. Not only would this likely have caused them to question the reliability of some of the evidence presented by the prosecution, it also may have elevated in significance certain aspects of the investigation that may otherwise have appeared unimportant. For instance, how did the police know to ask Tina Erti, the roommate of the victim's girl friend whether the victim possessed a small caliber gun with a pearl handle five days before a small caliber gun with a pearl-colored handle was found that was later determined to be the murder weapon? Did this suggest that the police had information that the victim had been shot with his own firearm, which would itself suggest the possibility that the victim was killed by someone he knew (or by someone assisted by someone he knew)? ...

"The motive offered by the Commonwealth -- that the defendant saw a police officer sleeping in his vehicle when he went to Walgreens to purchase diapers and hatched a scheme to kill him and take his service weapon as a trophy -- is not particularly compelling."

Prosecutors, however, beg to differ. In a statement, the Suffolk County District Attorney's office says:

"Never once in more than 20 years has a single piece of reliable evidence undercut the compelling case against Mr. Ellis, and we intend to present that case to a jury once again.

"As the SJC noted, not one shred of information developed since Detective Mulligan’s murder has contradicted the strong evidence on which Ellis was convicted. The court found that certain documents may have provided his first attorney with an alternative trial strategy, but none of them suggested actual innocence and many are inadmissible as evidence.

"The critical facts remain as true today as they were in 1993. Only two individuals were seen creeping toward Detective Mulligan’s vehicle before the murder and fleeing from it afterward. Only two individuals matched the physical descriptions of the murderers. Only two individuals were, by their own admissions, at the scene of the murder at the time it occurred, and only two sped away in a distinctive vehicle that was stripped of its identifying features after a description was made public."

In its arguments before the court, prosecutors argued there's really nothing new in the documents uncovered by Scapiccio through public-records requests. Ellis's attorneys during his trials, however, said that if some of the documents were listed on indexes handed to them, they never saw the actual documents.