Police in Michigan have arrested four people after a 5-year-old boy receiving treatment at The Oxford Center died when the hyperbaric chamber he was in exploded.

Three people have been charged with second-degree murder after a 5-year-old boy was killed when a hyperbaric chamber exploded at a medical facility in Michigan earlier this year, officials announced Tuesday.

Michigan Attorney General Dana Nessel has charged four people in connection with the death of a 5-year-old boy who was killed in a hyperbaric chamber explosion.

His mother was standing next to the chamber and suffered injuries to her arms when it exploded Jan. 31 Troy. Online court records show the center’s founder and chief executive, Tamela Peterson, is charged with second-degree murder.