Michael Mattioli pretrial postponed; state can't find key witness

In the case against former MPD Officer Michael Mattioli, prosecutors are unable to track down their key witness: the former chief medical examiner.

MILWAUKEE - In the case against former Milwaukee Police Officer Michael Mattioli, prosecutors are unable to track down their key witness.

Mattioli's pretrial Tuesday, Oct. 18 was cut short. He is charged with first-degree reckless homicide for the death of Joel Acevedo in 2020, accused of putting the man in a chokehold.

"There’s an issue I think, frankly, with the state's expert witness," said Milwaukee County Circuit Court Judge David Borowski.

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The state said it needs the witness – Dr. Brian Peterson, former chief of the Milwaukee County Medical Examiner's Office – to testify in order to prove cause of death. Peterson suddenly retired in September with no explanation, and the state said it is having trouble getting ahold of him.

"The state's request today is for the court to adorn the trial, so the state can determine whether or not Dr. Peterson will be the witness who testifies in this trial," said Ian Vance-Curzan with the Milwaukee County District Attorney's Office.

Dr. Brian Peterson

It could cause a delay in the trial. In court Tuesday, the judge asked Vance-Curzan if the doctor is not available – or not cooperating.

"I do know that we have talked to him, and that we are in the process of trying to personally serve him with a subpoena so that he would be here," said Vance-Curzan.

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Peterson's retirement also came amid staffing issues in the medical examiner's office; he spoke about it during a county meeting in September.

"At this point, we only have five staff pathologists, including myself," Peterson said at that time. "We do need six just to handle the workload that Milwaukee County offers and to stay within our accreditation standards."

Joel Acevedo

Borowski said he hopes the state can track down Peterson sooner rather than later. The district attorney's office told FOX6 News it is not aware of anything else being impacted by Peterson's retirement and, if Peterson isn't available, it would call another medical examiner. FOX6 reached out to Peterson, but did not immediately hear back.

Mattioli's pretrial is rescheduled for Monday, Oct. 24 and, as of now, the trial is still scheduled to start in November.