Fate of 4 charged in Michigan hyperbaric chamber death awaits judge ruling

DETROIT — Whether four people will stand trial in a lethal hyperbaric chamber fire that killed a 5-year-old boy last year is in the hands of a Troy judge.

The attorney general's office and each defendant's attorney made closing arguments Tuesday before 52-4 District Court Judge Maureen McGinnis. The arguments came in a preliminary examination, which determines whether a criminal defendant will face trial, that collectively stretched for more than a seven days since September.

Thomas Cooper underwent dozens of hyperbaric oxygen treatments at the Oxford Center in Troy for ADHD and sleep apnea. During a treatment Jan. 31, 2025, a fire sparked in the chamber, killing Thomas. State prosecutors charged Tammy Peterson, safety director Jeffrey Mosteller and operations manager Gary Marken with second-degree murder and involuntary manslaughter. Aleta Moffitt, the hyperbaric chamber's operator, faces charges of involuntary manslaughter and knowingly placing false information in a medical record.

The Oxford Center was a chain of medical facilities that offered hyperbaric oxygen treatments for a variety of conditions.

McGinnis said she will review what she heard during closing arguments and make her decision.

“I do need a little bit of time to take everything I’ve heard today," McGinnis said.

Prosecutors have centered their case on the allegation the Oxford Center at the time had not used grounding straps in the chambers, which connect a patient to the chamber to drain static electricity that may build up, including during Thomas' treatments.

Assistant Attorney General Chris Kessel argued the Oxford Center had a culture of following rules created by Peterson at the expense of the chambers operating safely. He returned to testimony by Andrew McMullen, a former employee of the company's Brighton location who testified Peterson told him that grounding straps were unnecessary and the Oxford Center did not use them, a change from when another former employee, Tiffany Hosey, started working for the Oxford Center in 2015.

"Did they know the rules? Did they now the consequences for not following the rules? And did they ignore them both? The answer is yes," Kessel said.

He argued Mosteller, Peterson and Marken ignored guidance from the chamber manufacturer's manual, the National Fire Protection Association and the Oxford Center's own training materials about safety in hyperbaric chambers, including proper grounding and appropriate clothing for the chambers to reduce fire risk.

The attorneys for each defendant disputed Kessel's argument that a culture of disregarding safety had been created at the center.

Moffitt's defense lawyer has contended she was never trained to use grounding straps on patients, nor did she have any knowledge of them or read the chamber manufacturer's manual. Ellen Michaels, Moffitt's attorney, suggested Moffitt has been caught up in a determination by the attorney general's office to assign accountability for Thomas' death.

“An accident occurred. Someone had to pay," said Michaels. "Public opinion said someone had to pay. The attorney general said someone had to pay. So in a very short amount of time, four people were charged.”

She said Moffitt was a conscientious, careful employee who cared about her patients, someone who "dotted every 'i' and crossed every 't.'"

“The picture that is painted of her does not support somebody who would act willfully, wantonly to put Thomas at risk," Michaels said.

She argued the charge against Moffitt for falsifying a medical record should not stand. Prosecutors accuse her of entering the end time of Thomas' treatment session in a log when he began the treatment. Moffitt is not a medical professional, said Michaels, and therefore can't create a medical record. Michaels claimed the chamber logs should be considered business records.

But Kessel said that Moffitt not knowing to use grounding straps should not release her from responsibility for Thomas' death. She had a responsibility to know the risks of operating machinery that could kill someone, Kessel said.

“She was the person who put Thomas in that chamber. ... She was the one who did not use a grounding strap," he said.

Marken's attorney, Todd Flood, disputed Marken had anything to do with decisions about patients or operating the chambers. He characterized his client's role at the Oxford Center as one akin to a handyman. Kessel alleged Marken was "part of this culture of Tammy Peterson's rules, which for some reason included not using grounding straps."

Flood said prosecutors have used an allegation that Marken manipulated a chamber's odometer, which recorded the number of cycles done in it, as a "red herring." Prosecutors have referenced the chamber was supposed to be retired after 20,000 hyperbaric "dives," but Peterson continued to use it past that point and allege that Marken tampered with the odometer with Peterson's permission.

“That’s a Jedi trick, judge," Flood said.

He noted Hosey, who testified for the attorney general's office, said on the stand Marken had nothing to do with the case.

Thomas Cranmer, who is defending Peterson, focused on testimony by Troy Deputy Fire Chief Shawn Hugg that his investigation into the fire's cause hasn't ended. He zeroed in on Hugg acknowledging, in response to Cranmer's questioning, that no evidence in the case confirms the chamber fire resulted from static created by Thomas' skin.

Prosecutors "want to start the analysis on third base. The real question is, can they even get to first base?” Cranmer said.

He suggested Peterson has been charged because of her status as the Oxford Center's CEO, rather than evidence she bears culpability for Thomas' death.

Kessel rebuffed that framing. Peterson faces charges because she made the calls about the center's protocols, he said. Kessel argued decisions at the Oxford Center flowed from her, and the staff all knew it.

"Tammy Peterson was the boss. Capital 'T,' capital 'B,'" he said.

McGinnis said she hasn't decided whether to issue a ruling from the bench or in writing.

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