Nearly two decades after Sean Ellis was convicted in the gruesome 1993 murder of a Boston police detective, a defense lawyer is preparing to tell a Suffolk Superior Court judge that the jury did not hear key evidence that might have changed its verdict.

Defense lawyer Rosemary Scapicchio said in her motion for a new trial that recently discovered evidence links the victim, John Mulligan, to a conspiracy in which Boston police officers allegedly robbed drug dealers. This connection, she said, reveals a new motive for the murder and perhaps a different killer.

The hearing is scheduled for Thursday, Scapicchio said.


According to Scapicchio’s motion, the new evidence details “that the Boston Police Department was aware that multiple police officers believed that the victim in this case . . . was actually killed by another identified police officer.”

Scapicchio wrote that she obtained the evidence from FBI files through the Freedom of Information Act.

“The trial evidence against Ellis was created by powerful but corrupt Boston police officers that were intent on covering up their own crimes and the crimes of the victim, thereby covering up other potential suspects as well as hiding the truth from the defense and the jury,” Scapicchio wrote.

On Saturday, Jake Wark, spokesman for Suffolk District Attorney Daniel Conley, dismissed Scapicchio’s argument as groundless.

“Nothing in this latest motion challenges the strong evidence that proved Ellis’s guilt at trial. The state’s highest court affirmed his conviction, and it should remain in place,” he said.

Mulligan, 52, was shot five times in the face with a .25-caliber pistol while working a uniformed, paid detail at a Walgreens pharmacy on American Legion Highway in Roslindale in the early morning of Sept. 26, 1993.

A 27-year veteran of the police force, Mulligan was sitting in his rented sport utility vehicle in front of the store, apparently sleeping, when he was murdered.


His 9mm Glock service pistol was stolen; prosecutors said Ellis had wanted the gun as a trophy.

Despite evidence that Ellis had the murder weapon and Mulligan’s service pistol in his possession after the killing, his first two trials ended in hung juries. Ellis was convicted of first-degree murder in the third.

Richard Mulligan, the victim’s brother, scoffed at Ellis’s chances for a new trial. Ellis, 39, is serving a life sentence without parole.

“The jury heard all the evidence. It’s compelling evidence that convicted him,” Mulligan said in a phone interview Saturday. “They placed him at Walgreens; they placed him in the parking lot; they found John’s service revolver in his possession. These guys think that the general public are a bunch of fools.”

Ellis, who was 19 at the time of the killing, said he had been shopping for diapers that night after receiving a ride from Terry Patterson, a friend. Ellis told authorities he saw Mulligan alive in his SUV, which had been parked in the fire lane just outside the store.

Patterson was convicted separately but later granted a new trial when the state Supreme Judicial Court ruled in 2000 that his lawyer would have served her client better as a defense witness. Patterson pleaded guilty to manslaughter and was released from prison in 2007.

During their trials, Ellis and Patterson each accused the other of the killing.

A key prosecution witness against Ellis was Rosa Sanchez, a teenager whose aunt had dated Kenneth Acerra, a detective and a friend of Mulligan’s who was involved in the investigation.


At first, Sanchez identified a man other than Ellis as the man she saw outside the drug store that night.

But after a conversation with Acerra and his partner, Walter Robinson, she chose Ellis from an array of photographs.

At trial, Sanchez testified that she saw Ellis crouching next to Mulligan’s vehicle before the officer was killed.

The new evidence, Scapicchio said in the motion, shows “a true picture of Mulligan and his cohorts who were simultaneously acting as detectives, criminals, and the men that investigated this crime.”

In 2000, the state’s high court upheld Ellis’s conviction and rejected a motion for a new trial.

The justices ruled that his defense attorneys had not offered any direct evidence that Sanchez, Acerra, and Robinson had acted corruptly in the case.

Acerra and Robinson pleaded guilty in 1998 to federal corruption charges. That case was not tied to the Mulligan murder.

Brian MacQuarrie can be reached at macquarrie@globe.com.