A Troy police detective's testimony before four Oxford Center employees were charged sheds new light on the explosion that killed Thomas Cooper.

Prosecutors said a safety manager at the Oxford Center conducted “his own experiments” on a hyperbaric chamber to prove to employees it was safe prior to a deadly explosion that killed a 5-year-old boy.

Oxford Center CEO Tami Peterson was arraigned on a charge of second-degree murder Tuesday after a 5-year-old boy died in a hyperbaric chamber explosion at the facility earlier this year.