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Controversial ex-Milwaukee medical examiner taken off Mattioli trial witness list



Dr. Brian Peterson, chief medical examiner for Milwaukee County, is pictured outside the Milwaukee County Medical Examiner's Office in 2020.

A name that caused a massive shakeup in Milwaukee County’s judicial system a year ago briefly resurfaced in the lead-up to a homicide trial that started Monday — former Milwaukee County Medical Examiner Dr. Brian Peterson.

Prosecutors had called Peterson as an expert witness in the trial of former Milwaukee police officer Michael Mattioli, who was charged with first-degree reckless homicide in the death of Joel Acevedo in April 2020, while Mattioli was off-duty.

Late Friday, Peterson was removed from the witness list and was replaced with Milwaukee’s current chief medical examiner, Wieslawa Tlomak.

Here’s what to know about Peterson and his role in the Mattioli case so far:

Peterson’s failure to appear in court caused Mattioli trial delay

The Mattioli trial was set to be heard last fall but was delayed due to Peterson’s failure to appear in court.

At that time, prosecutors filed motions to adjourn at least two other cases due to Peterson not being present to testify.

This was shortly after Peterson had suddenly resigned from his long-held position as one of Milwaukee County’s highest-paid officials.

Peterson and Milwaukee County Executive David Crowley declined to comment on the reason for his departure and the effect it had on the backlog of homicide cases in the courts.

Peterson previously served with Marines, worked in California and Waukesha

Peterson grew up in Brookfield, later earning his M.D. from Medical College of Wisconsin in 1980. He interned at the Medical College of Ohio in Toledo, Ohio.

Before joining the Milwaukee County Medical Examiner’s Office in 2008, he worked at the Waukesha County Medical Examiner’s Office and as president of Forensic Medical Group, Inc. that provided autopsy services for counties in northern California. He had also served as a medical officer with the Marines.

Peterson was Milwaukee County’s chief medical examiner for 12 years

He was appointed as the Chief Medical Examiner for Milwaukee County in 2010 after the resignation of Christopher Happy.

In 2021, Peterson’s pay totaled $261,714.

On Sept. 19, 2022, Peterson filed “emergency retirement” paperwork with Milwaukee County. He provided no explanation for his sudden departure.

Medical examiners investigate sudden deaths and suspected homicides

A medical examiner is an officer appointed by the County Executive and/or the County Board of Supervisors who carries out investigations and examinations of people who have died suddenly, unexpectedly or violently.

Some counties have coroners who fulfill much the same duties but are elected instead of appointed.

“Wisconsin is one of a handful of states that doesn’t require training for coroners and medical examiners,” a 2014 Green Bay Press-Gazette article noted. “Critics say that means the only real requirements for elected coroners is that they receive more votes than anyone running against them.”

The medical examiner is often called on to testify at homicide trials as to cause and manner of death, based on autopsies of victims.

Questions were raised about Peterson’s sudden retirement

According to paperwork filed with the county, Peterson retired.

But during the delay of the Mattioli trial, the prosecuting attorneys told the court they had learned that Peterson has been terminated from his job.

“So, now apparently Dr. Peterson was terminated by the county executive?” asked Milwaukee County Circuit Court Judge David Borowski before the court. 

The county executive’s then-spokesman, Brandon Weathersby, told the Journal Sentinel at the time that Crowley had signed off on Peterson’s retirement and had no further comment.

Attorneys decried Peterson’s disappearance

Attorney B’Ivory LaMarr, who is serving as counsel for the Acevedo family in the Mattioli trial, previously called for the county to devise a contingency plan following Peterson’s disappearance.

“When you’re dealing with cases when justice is on the line, it should not be delayed because of looking to find a state witness or county witness,” LaMarr told the Journal Sentinel. “I do have several other wrongful death cases and it’s almost causing me to go back now to find out who the actual medical examiner was … because if it’s Peterson, I might need to be concerned.”

LaMarr also noted the impact it had on families still awaiting answers.

“I think that it causes even further harm to families,” he said. “It affects the grieving process. It definitely, completely results in them reliving the situation and the circumstance — it delays their ability to get closure.”

Last year, Milwaukee defense attorney Daniel Adams also questioned Peterson’s disappearance:

“As one of the highest-paid county employees, I believe he owes a duty to the taxpayers to show up, subject to a subpoena and subject to his role as the top forensic medical examiner for the community,” he said.

Ian Vance-Curzan, an attorney with the Milwaukee County District Attorney’s Office, had also requested Borowski adjourn the trial so that the state could determine whether Peterson would be the witness who would testify in the Mattioli trial.

At that time, the state was trying to subpoena Peterson.

During that same hearing, Borowski told the court: “There’s an issue I think, frankly, with the state’s expert witness.”

Peterson was on witness list in the Derek Chauvin trial

In 2021, Peterson was retained as a potential expert for the defense in the trial of former Minneapolis police officer Derek Chauvin.

Chauvin was eventually convicted of unintentional second-degree murder, third-degree murder and second-degree manslaughter in the killing of George Floyd, who died after Chauvin kept his knee on Floyd’s neck for more than nine minutes.

Prosecutors said Floyd died from lack of oxygen as a result of Chauvin kneeling on his neck. The defense had raised the question of how much Floyd’s drug use and prior health conditions played a role in his death.

Peterson wasn’t called to testify.

Peterson criticized a study that found racial bias in forensic pathology

In 2021, a study in the Journal of Forensic Sciences in February examined how often Black and white infants’ deaths were ruled homicides.

The study suggested that medical examiners’ roles in the criminal justice system might be more subjective than usually presumed, as well as being influenced by cognitive bias.

The study drew criticism from Peterson and other individuals within the field of forensic pathology at the time.

On a Listserv for pathologists shared with the Journal Sentinel, Peterson called out the study’s assertion that “cause of death” findings are basically objective, “based on tests and observations well-grounded in medicine.”

Peterson responded, “I think we all know that that is basically nonsense.”

“What is woke today is fodder tomorrow,” Peterson wrote. “Is there anyone in our profession that has not, at one point or another, quipped about ‘spinning the wheel of death’ and picking one?

“How many cases do we see in which there are multiple competing causes of death, any one of which, or combination, would work just fine?”

He wrote: “I could go on … but I suspect that under the suppositions common to CRT (critical race theory) these days, by protesting, I am merely proving my own bias. There is no logical defense at this point.”

Peterson was also joined by two other experienced medical examiners, David Fowler and William Oliver, who called the study “fatally flawed” and asked The Journal of Forensic Sciences to retract the publication.

Fowler, the former chief medical examiner for Maryland, testified for Chauvin’s defense, saying that the officer’s knee on George Floyd’s neck was not a main cause of his death.

The New York Times also reported that Peterson had filed an ethical complaint against the four forensic pathologists who assisted the cognitive neuroscientist who led the study — one of whom, Joye Carter, consulted with the prosecution in the Chauvin case.

Peterson accused the four other physicians of “conduct adverse to the best interests and purposes” of the profession, according to the Times, which had obtained a copy of the confidential ethics complaint.

“By basically accusing every member of ‘unconscious’ racism, a charge impossible to either prove or refute, members will henceforth need to confront this bogus issue whenever testifying in court,” Peterson wrote.

Contact Vanessa Swales at 414-308-5881 or Follow her on Twitter @Vanessa_Swales.

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