Jeffrey Mosteller, the safety director at the Oxford Center in Troy, pleaded no contest on Tuesday, July 21, to involuntary manslaughter in the death of 5-year-old Thomas Cooper, who was killed when a hyperbaric oxygen chamber caught fire and exploded during treatment on Friday, Jan. 31, 2025.

Mosteller, 65, of Clinton Township, is the first of four Oxford Center employees charged in the case to resolve his criminal charges. A second-degree murder count was dismissed as part of the plea deal, which calls for a prison sentence of 19 months to 15 years, according to a statement from the Michigan Attorney General's Office.

Oakland County Circuit Judge Kwamé L. Rowe will consider the sentencing agreement at a hearing in August.

Thomas had been undergoing his 36th hyperbaric oxygen treatment for ADHD and sleep apnea at the Oxford Center's Troy location when prosecutors say a spark of static electricity triggered a fireball inside the pressurized chamber. His mother was burned on her arm trying to pull him out. She could not reach him in time.

Prosecutors alleged Mosteller deliberately disregarded safety protocols published by the National Fire Protection Association and Sechrist, the chamber's manufacturer. Prosecutors said he conducted his own experiments at the center's Troy and Brighton locations in an attempt to prove grounding straps were unnecessary to discharge static electricity, even though industry standards, manufacturer manuals, and the center's own training materials required them.

Former Oxford Center employee Tiffany Hosey, who testified she was fired after raising safety concerns, told the court the center did not use grounding straps during treatments. Hosey said CEO Tamela Peterson told her the straps were not used because Peterson considered them a strangulation risk for children.

Michigan Attorney General Dana Nessel said in a July 21 statement that Mosteller "allowed an outdated device to operate in defiance of safety standards."

Mosteller's attorney, Alona Sharon, declined to comment after the plea, according to the Detroit News.

A no contest plea is not an admission of guilt but is treated as such for sentencing purposes. It can also provide some liability protection in civil cases.

Three co-defendants still face charges. Peterson, 59, of Brighton, the Oxford Center's CEO and founder, and Gary Marken, 66, of Spring Arbor, the operations manager, are each charged with second-degree murder and involuntary manslaughter. Aleta Harward Moffitt, 61, of Rochester Hills, the technician operating the chamber when the explosion occurred, faces involuntary manslaughter and a charge of placing false information on a medical record.

Marken and Moffitt are scheduled for a pretrial hearing on Monday, July 27. Peterson had a separate motion hearing on Wednesday, July 22.

Thomas Cooper's parents, James and Juana Cooper, filed a $100 million wrongful death lawsuit on Monday, Sept. 22, 2025, in Oakland County Circuit Court naming eight defendants, including all four criminal defendants, the Oxford Center, and chamber manufacturer Sechrist Industries.

The Oxford Center offered hyperbaric oxygen therapy for conditions including ADHD, sleep apnea, and autism. The facility was not accredited by the Undersea and Hyperbaric Medical Society, and the FDA has not approved hyperbaric oxygen therapy for those conditions.

Residents with information related to the case can contact the Michigan Attorney General's Office at 517-335-7622.