More witnesses took the stand in the 52-4 District Court in Troy on Friday in the preliminary examination for the deadly hyperbaric chamber explosion that killed 5-year-old Thomas Cooper back in January.

Tamala Peterson, Gary Marken, Alita Moffitt and Jeffrey Mostellar are accused of not following safety protocols while working at the Oxford Center in Troy. 

As part of the preliminary examination to determine whether all four of the defendants will go to trial, the lead police and fire investigators on the case, Troy Police Detective Danielle Trigger and Troy Deputy Fire Chief Shawn Hugg, shared their findings.

"After I reviewed the video, there was no evidence of any type of device or item brought in by the victim."

"All of the training documentation that we recovered from the Oxford Center indicates that wrist straps are to be utilized, and they were available at the facility," said Trigger.

During cross-examination, defense attorneys for Peterson and Moffitt asked questions on the need for using grounding straps and what evidence was found to conclude the cause of the explosion.

"The only source of electrical fire that we identified was the electrical components within the control panel, as well as the speakers within the main door," said Hugg.

Investigators say the boy was inside one of their hyperbaric chambers receiving treatment when video footage shows it catching fire.

While they concluded the cause was due to static electricity from the system paneling, defense attorneys pushed back on whether other reasons could be a factor.

"And so, bottom line, you cannot rule out fabric-to-fabric static as a cause of this fire. Isn't that true? That's true," said Hugg.

Testimony is expected to resume on Dec. 16.