4 people accused in the fatal explosion that killed Thomas Cooper in a hyperbaric chamber at Oxford Center in Troy, Michigan

Four individuals are facing charges in connection with the tragic death of a 5-year-old boy in a pressurized oxygen chamber that exploded at a medical facility near Detroit.

The incident took place at the Oxford Center in Troy, where Thomas Cooper, a young boy from Royal Oak, Michigan, lost his life. His mother, who was present at the scene, sustained arm injuries during the explosion on Jan. 31.

According to online court records, Tamela Peterson, the center’s founder and CEO, has been charged with second-degree murder. The other accused individuals are Gary Marken, 65, and Gary Mosteller, 64, who face charges of second-degree murder and involuntary manslaughter. Aleta Moffitt, 60, is charged with involuntary manslaughter and the intentional falsification of medical information on records.

Arraignments were scheduled Tuesday afternoon in Troy District Court, Lt. Ben Hancock said. The case is being prosecuted by Michigan Attorney General Dana Nessel and details were expected to be released during a late morning news conference.

Raymond Cassar, Marken’s attorney, said the second-degree murder charge comes as “a total shock” to him and his client.

The video in the player above is from an earlier report.

“For fairness, he is presumed innocent,” Cassar said. “This was a tragic accident and our thoughts and our prayers go out to the family of this little boy. I want to remind everyone that this was an accident, not an intentional act. We’re going to have to leave this up to the experts to find out what was the cause of this.”

Moffitt’s lawyer, Ellen Michaels, declined to comment before Tuesday’s arraignment. The Associated Press left a telephone message Tuesday morning seeking comment from Peterson’s attorney. An attorney was not listed for Mosteller.

A voicemail was left seeking comment from an attorney representing the Oxford Center. The AP also left a message seeking comment from the center.

The Oxford Center had said in an email following the explosion that a fire started inside the hyperbaric oxygen chamber.

“The safety and wellbeing of the children we serve is our highest priority,” the center said. “Nothing like this has happened in our more than 15 years of providing this type of therapy. We do not know why or how this happened and will participate in all of the investigations that now need to take place.”

Hyperbaric therapy increases delivers pure oxygen to a person’s body inside the pressurized chamber. That’s up to five times the amount of oxygen in a normal room, Troy Fire Lt. Keith Young said following the explosion.

“The presence of such a high amount of oxygen in a pressurized environment can make it extremely combustible,” Young said. “We did some initial investigation. This is very uncommon, so we’re not sure what led up to it.”