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.

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. Thomas Cooper died on Jan. 31 in the incident at the Oxford Center in Troy, officials said.

Two other people were arrested Monday and also are expected to be arraigned in the child's death, police said.