Sean Ellis: Pool photo by Jesse Costa/WBUR

In 1993, Boston Detective John Mulligan was brutally murdered with five shots to his face as he slept in his parked SUV outside a Roslindale Walgreens.

In 1995, Suffolk County prosecutors convicted Dorchester’s Sean Ellis of murder and armed robbery in his third trial, after his first two trials ended in hung juries. He was 19 at the time of the crime.

Last week, in a stinging rebuke to Boston Police and prosecutors of that era, Superior Court Judge Carol S. Ball reversed those convictions and ordered a retrial for Ellis, now 40, citing prosecutorial failures and bias by corrupt investigating detectives.

Newly unearthed evidence, withheld from Ellis’s attorneys, has revealed that Detective Mulligan participated in armed robberies of drug dealers with three Area E-5 colleagues, Kenneth Acerra, Walter Robinson, and John Brazil. Because these men were “involved in nearly every aspect of the homicide investigation that led to Ellis’s prosecution,” Judge Ball ruled that defense attorneys should have been able to make the argument that, in a “rush to judgment,” the corrupt detectives railroaded Ellis to end the probe into Mulligan’s police work before it “turned in their direction.” One robbery by Acerra, Robinson, and Mulligan occurred just two-and-a-half weeks before his murder.

Acerra and Robinson were imprisoned in 1998 for their felonies; Brazil escaped prosecution by turning evidence. Their taint of the Mulligan investigation has not been acknowledged until now.

Suffolk County DA Daniel F. Conley has vowed to fight on, citing “direct, reliable, and corroborated evidence” against Ellis. I disagree. As someone who knew Sean Ellis as a Metco student in Needham, I’ve followed his case closely for the past 22 years and have concluded that the case against him is remarkably weak.

Sean admitted being at Walgreens that morning and spoke voluntarily to police, explaining he bought diapers for a relative. Police found his box of Luvs with its timed and dated receipt. As his defense attorney, Rosemary Scapicchio, notes, would you place yourself at a murder scene with a receipt unless you knew you were innocent?

A co-defendant, Terry Patterson, pleaded guilty to manslaughter in Mulligan’s death. Sean stands convicted of helping to hide guns for Patterson after the crime (as did three other individuals who were granted immunity from prosecution). Evidence hiding is accessory after the fact — not murder one.

There was no physical evidence connecting Sean to the slain detective. The only ID of him was made by a teenager — with family ties to Detective Acerra— who said that 45 minutes before the murder, she saw an African–American youth peering into Mulligan’s car window as he slept. She identified Sean from photos, but only after first identifying another man. Her second look at the photos, when she fingered Sean, was engineered by Acerra and Robinson.

The known tactics of those later-convicted felons should have raised questions: Robinson removed cash from Mulligan’s closet immediately after the murder— money never reported to the department (drug money, Ellis’s attorney alleges). Acerra discovered Mulligan’s personal cell phone, initially reported as stolen from his SUV, a full week after the murder in a “secret compartment” in the vehicle’s console. By then there was no record of calls and no fingerprints -- not even Mulligan’s. Yet a woman who’d dated Mulligan testified that two detectives visited her after the murder saying she was the last person called from his phone. “So someone had those numbers,” attorney Scapicchio points out.

Acerra and Robinson never should have been on the task force to begin with, Judge Ball concluded. Allegations within the department of their armed robberies, at least one involving Mulligan, constituted “significant corruption” for which then-Police Commissioner William Bratton and his successor, Paul Evans, “should have been apprised.” But the higher ups turned a blind eye to the detectives’ misconduct.

Only Assistant District Attorney (now retired Judge) Phyllis Broker, the chief prosecutor in the case, cried foul – for which she won Judge Ball’s praise. Following Acerra’s “discovery” of Mulligan’s cell phone, Broker pulled him from the task force; after the unorthodox photo- viewing procedure involving Acerra’s family relative, Broker had him and Robinson give taped statements explaining the circumstances.

But Phyllis Broker was muzzled. The Detectives Union objected to her accusations of Acerra and Robinson and demanded her removal, and the Boston Globe reported that at “a hastily-called meeting with Police Commissioner William J. Bratton... it was agreed that Broker would continue with the case -- but that there would be no further questioning of the detectives...”

“No further questioning of the detectives...direct, reliable, corroborated evidence.”

It sounds to me like a continuing thin blue line.

Please, Mr. Conley, no thin blue line in 2015. Not with the public’s diminished confidence in law enforcement agencies. Judge Ball expressly noted that today’s Boston’s law enforcement culture is much improved over that permeating the Mulligan case: “Twenty years after these events, this judge is acutely aware of the strides made by the Boston Police Department in the professional handling of the investigation and prosecution of their cases.” Why order a fourth trial for Sean Ellis and fall on your sword for the lapses and corrupt conduct of a previous regime?

Elaine A. Murphy is a former Boston English teacher and retired publications editor. She has created a website on the Mulligan case: justiceforseanellis.com.

Statement from District Attorney Daniel Conley's office by Jake Wark:

"Under District Attorney Conley, this office has earned a national reputation for identifying, correcting, and preventing wrongful convictions. This administration has never shied away from reversing a miscarriage of justice. But in our judgment, this was a conviction based on direct, reliable, corroborated evidence. We fully intend to present that evidence to a new jury if necessary...

"In 20 years, not one person has produced actual evidence of killers other than Sean Ellis and Terry Patterson. To date, they remain the only individuals who were at the scene before the murder, were linked to a car that sped from the scene after the murder, and possessed the firearm used during the murder. In fact, with Patterson's unequivocal admission of his role in Officer Mulligan's homicide, and with Ellis' trial conviction for possessing both the murder weapon and Officer Mulligan's service firearm remaining in place, the record only supports Ellis' guilt."