Thomas Cooper from Royal Oak, Michigan, was pronounced dead at the scene. His mother was standing next to the chamber and suffered injuries to her arms when it exploded Jan. 31 at the Oxford Center in Troy.

Three people were charged with second-degree murder and a fourth person was charged with involuntary manslaughter in the death of Thomas Cooper, 5.

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