OAKLAND COUNTY, Mich. – The lead officer in the Oakland County hyperbaric chamber explosion case testified about responding to the scene and recovering evidence as preliminary hearings continued for the four workers charged after a 5-year-old boy’s death.
Tamela Peterson, 58, of Brighton, Jeffrey Mosteller, 65, of Clinton Township, Gary Marken, 66, of Spring Arbor and Aleta Moffitt, 60, of Rochester Hills, were charged after Thomas Cooper, 5, 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.
All four workers appeared in 52-4 District Court before Judge Maureen McGinnis on Tuesday, Dec. 2, 2025, for a continuation of their preliminary examinations.
Two days of the hearing were held in September, and it continued on Monday, Dec. 1, and Tuesday, Dec. 2, 2025.
Previous coverage --> Testimony says 5-year-old’s hyperbaric chamber death at Oxford Center was preventable
One of the witnesses called on Tuesday was Troy Police Det. Danielle Trigger, the officer in charge of this case.
You can watch Trigger’s testimony from Dec. 2, 2025, in the video at the top of this article.
Trigger testified that she was the on-call investigator on Jan. 31 and had overheard a dispatch run to the Oxford Center in Troy for a reported explosion. She and other investigators responded to the scene and said they arrived shortly after EMS and road officers arrived at the scene.
Arriving at the ‘chaotic’ scene
She describes arriving at the scene as “chaotic,” and recalled “distraught” staff outside the center.
When she went into the center, she said firefighters were working inside a room that had three hyperbaric chambers, noting that the middle chamber, the one where the explosion had occurred, was “visibly very burnt.”
Trigger said what appeared to be a gurney was pulled out of that chamber, and the child’s body was “burnt severely” and “unrecognizable.”
While at the scene, Tigger said she didn’t interview Moffit, but said Peterson arrived a short time after law enforcement arrived at the scene. Shortly after that, Trigger said Mosteller arrived, and that she never saw Marken at the scene that day.
Trigger said she heard Peterson say the manufacturer had to get out there to figure out what had gone wrong “because they do everything by the book.”
Recovering items from the facility
At the scene, investigators recovered medical records, maintenance logs, and the user manual for the chamber involved. Trigger reviewed the manual and noted that the wrist grounding strap pictured was not used during the incident, as confirmed by video footage.
Trigger returned to the police department after attending the autopsy and continued reviewing records, determining that grounding wrist straps did not appear to be common practice at the facility.
During the investigation, Trigger drafted search warrants and recovered extensive training materials from the Oxford Center, including documents emphasizing fire prevention, safety protocols, and the critical importance of grounding patients with wrist straps.
One training manual warned that in the event of a fire in a monoplace chamber filled with 100% oxygen, survival chances for the patient are virtually nonexistent, underscoring the need for prevention.
The chamber that exploded was a monoplace chamber. Throughout expert testimony, we’ve learned that the concentration of oxygen that pressurizes multiplace chambers (Class A) is 21%, while the concentration of oxygen in monoplace chambers (Class B) is generally around 100%.
Other training materials and documents recovered had multiple sections that included making sure a grounding strap was secured, emphasizing the importance of one being used.
Trigger was also asked by Assistant Attorney General Chris Kessel to look at a picture from a document recovered at the Oxford Center, which was a photo of a child with hair that appears to be rising.
The detective said that video footage showed the boy’s hair rising just before the explosion, consistent with the buildup of static electricity.
Grounding wrist straps found in ‘junk drawer’
She noted that grounding wrist straps were found unused in a drawer at the facility that she described as being a “junk drawer,” as it also contained half-eaten bags of chips and tape.
Trigger said the wrist straps appeared as though they hadn’t been used or touched in some time.
Certification isn’t required to operate a hyperbaric chamber in Michigan. Trigger testified that Mosteller had a current certification, though. Multiple attorneys objected to this testimony, saying it wasn’t relevant because certification isn’t required in the state, but the judge found the information to be relevant, since those certified would have had to be exposed to training materials, which she said is relevant to the case.
Questions about evidence being shared
Trigger also explained how detectives upload materials related to investigations into Evidence.com, which allows them to create a link to share with others, including prosecutors and defense attorneys.
Then, if additional items are added, detectives are prompted with the opportunity to share new items with any party who previously received the link.
Since Trigger first created and shared the link to the materials, she said about eight or nine items were added, including information about bond violations for one of the defendants, the fire report, the autopsy report and supplemental reports that were created after a taint team reviewed electronic devices.
Although Trigger sent the updated links to the defense attorneys, they said they never received them. This appeared to be some sort of glitch with the platform, since the detective had verification on her end that it was sent.
Kessel said the attorney general’s office personally sent some of the documents to the defense attorneys, including the autopsy report and the fire report, so they should have most of the materials.
Cycle counts, maintenance records
During Trigger’s cross-examination, questions about cycle counts on the chambers came up, and the detective was asked about how she investigated the chambers.
Todd Flood, Marken’s attorney, asked her if they had discovered whether any of the chambers had done 3,000 cycles in a four-month period, and Trigger said they only investigated the chamber where the explosion occurred, but the facility didn’t keep a log of the chambers, so she couldn’t speak to how many cycles were done in that time period.
Alona Sharon, Mosteller’s attorney, asked her about finding wrist straps, as well as about the number of dives (treatment sessions) that had been done on the chamber where the explosion occurred.
Trigger said that in the span of nine years, the chamber accrued over 20,000 dives, based on the evidence.
Additionally, a maintenance record from December 2022 indicated that Sechrist Industries, the manufacturer of the chambers, said they would no longer service the chamber because it had over 20,000 dives.
The preliminary examinations are scheduled to continue at a later date, and the cross-examination of Trigger will continue.