OAKLAND COUNTY, Mich. – The preliminary hearing in the Oakland County hyperbaric chamber explosion case continued Friday, revealing details about phone calls that ended a police interview with a defendant and the investigation into the cause of the fire.
Tamela Peterson, 59, of Brighton, Jeffrey Mosteller, 65, of Clinton Township, Gary Marken, 66, of Spring Arbor and Aleta Moffitt, 61, of Rochester Hills, were charged after Thomas Cooper was killed when the hyperbaric chamber he was receiving treatment in exploded at the Oxford Center in Troy on Jan. 31, 2025. The boy’s mother was also injured in the explosion.
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The four workers are accused of ignoring several safety guidelines for operating hyperbaric chambers, including not using a grounding wrist strap, rolling back the chamber cycle count, giving the 5-year-old boy a blanket straight from a running dryer, using polyester pillows and more.
The CEO and three workers appeared before Oakland County Judge Maureen McGinnis in 52-4 District Court on Friday, Dec. 12, for a continuation of their preliminary examination.
The purpose of a preliminary examination is to determine if a felony was committed and if there is probable cause to send a defendant to a higher court, where they could then face trial.
Two days of the hearing were held in September, and two more were held on Dec. 1 and Dec. 2.
For a full deep dive into what we learned during previous days of the preliminary hearing, check out the following stories:
Following Friday’s hearing, the preliminary examination is expected to continue again on Tuesday, Dec. 16, 2025.
Here’s everything we learned in court on Friday, Dec. 12:
The court day began with the defense attorneys continuing to cross-examine Troy Detective Danielle Trigger, who was the officer in charge of the case.
She previously testified about reviewing training materials found at the facility and the grounding wrist straps that were discovered in a “junk drawer” at the Oxford Center at the scene.
During the cross-examination, Alona Sharon, Mosteller’s attorney, asked Trigger about when she and another detective had interviewed Mosteller at this home.
Interview with Mosteller
She said they knocked, and Mosteller let them in. They interviewed him for about three hours, and Trigger agreed that overall, he was cooperative and didn’t decline to answer any questions.
But then, Mosteller received two phone calls.
Trigger said one of the phone calls was from a woman named Pam. This was a friend of Mosteller’s that he had been living with at the time.
Phone calls: ‘Tell them to leave’
The detective said she heard the woman say, “Tammy said to tell them to leave and don’t say another word.”
After that phone call, he received one from Peterson, and after receiving that call, Mosteller wanted to terminate the interview, Trigger said.
Trigger also testified that she did not ask Mosteller if he used the chamber or wrist straps himself.
When asked if knowing whether he used either of these items would have been important to her, Trigger said, “No.”
“At that point, we had established what appropriate safety protocols were, and him not utilizing them would not have been relevant in our mind.”
Sharon said Mosteller told police that he believed the chamber was safe without a wrist strap, and Trigger said, “He also told us that he doesn’t know of a single other person in the industry who operates that way in his 41 years of experience.”
Moffitt’s role at the Oxford Center
Ellen Michaels, Aleta Moffitt’s defense attorney, asked Trigger if her client was in charge of creating safety protocols at the Oxford Center, and Trigger agreed that she was not.
Moffit was the technician who was operating the chamber at the time it exploded, killing Thomas.
Testimony revealed that other people had operated the chamber for some of Thomas’ other treatment sessions, which are also called dives.
Trigger said that wrist straps were never used for any of his 30+ treatments.
They also discussed the times that were noted for each dive in a logbook, which is related to the falsifying medical records charge that Moffitt received.
Error in log time for boy’s treatment session
Dive records showed discrepancies in logged times, including a false entry on Jan. 31, 2025, where the recorded surface time (end time) was after the explosion had already occurred.
Michaels argued that previous testimony revealed that Oxford Center staff would sometimes prefill in the end time for the session, since there was a set amount of time for each dive.
Moffitt took immediate action when the chamber exploded, attempting to manage the situation and help the other patient who was receiving treatment out of the other chamber, but once firefighters arrived, they were all asked to leave, and she was never able to enter the chamber room again to fix the end time she recorded, according to testimony.
Trigger testified that no medical professionals were on site at the time of the explosion, and neither Moffitt nor another staff member present had medical or hyperbaric certifications. There is no evidence that Moffitt received formal training or certification.
When Trigger testified that Michaels was not a medical professional, Michaels questioned if that was the case, how could she be charged with falsifying a medical record, to which Assistant Attorney General Chris Kessel objected due to it being a question that asked Trigger to draw legal conclusions.
During Kessel’s redirect, Trigger confirmed that hyperbaric chamber treatment is considered a medical treatment. She testified that Moffitt was not forced to fill out the Jan. 31 form with the wrong time.
At the scene, multiple chamber logs and checklists were found, but the logbook for the chamber that had exploded was missing, according to testimony.
Large increase in cycle counts
Trigger found no clear explanation for a large increase in the number of dives recorded for the chamber that exploded.
When Peterson was informed that the cycle count was over 20,000, she asked for proof, according to Trigger.
Trigger said Peterson was sent a document from Sechrist Industries, the manufacturer of the chambers, that indicated it was at over 20,000 cycles.
But Trigger said Peterson didn’t dispute this number in her response, but instead said that the center had sold the chamber and that it was no longer in use.
Deputy fire chief testifies
Troy Fire Department Deputy Chief Shawn Hugg testified about securing the Oxford Center after the explosion and his investigation into the cause of the fire.
He said he examined the chambers, including the one that exploded and its control panel. Hugg also reviewed lab and expert reports, video footage, and operational manuals.
Following the explosion, Hugg also said that he opened the center for other parties involved in a civil case related to the incident under a court order issued by a different judge.
Fire classified as accidental
The fire was classified as accidental because there was no evidence of human intervention or intention to start the fire, or electrical faults in the chamber’s control panel or speakers.
Thomas also did not possess any items that could have caused the fire while he was in the chamber, according to video footage, and was not wearing a grounding wrist strap.
The investigation concluded static electric discharge as the likely cause, meeting all five conditions necessary for a static-induced fire ignition.
During cross-examination, Hugg acknowledged he is not an expert in hyperbaric medicine, electrical engineering, or electrostatics, and that the investigation remains open with some evidence yet to be tested, including the bulk oxygen storage cylinder. A sample from this has been requested to be tested.
Evidence still to be tested
When a defense attorney asked if impurity in the oxygen could be connected to the fire, Hugg said it was possible. When the attorney further inquired if this could be ruled out as a potential cause of the fire, Hugg said, “Specifically, no.”
He emphasized the use of NFPA 921, the Guide for Fire and Explosion Investigations, as the industry guide used to determine the origin and cause of fires and explosions.
The deputy fire chief also agreed that grounding straps do not eliminate the production of static.
A defense attorney said, “You cannot rule out fabric-to-fabric static as a cause of this fire. Is that true?” Hugg said, “That is true.”
At that point in the testimony, it had reached the time the hearing was supposed to end for the day.
Next court date
Defense attorneys will continue to cross-examine Hugg on Tuesday, Dec. 16, 2025, when the hearing resumes.