TOMS RIVER, N.J. (AP) — The murder trial of a New Jersey dad charged in the death of his 6-year-old son has begun with prosecutors and defense lawyers disputing what caused the boy’s death.

Ocean County prosecutors argue that Corey Micciolo died from blunt force trauma he suffered when Christopher Gregor, 31, forced him to run on a treadmill in March 2021. The workout was captured on surveillance video which shows Gregor continually increasing the treadmill’s speed, causing his son to fall off off it face-first about six times.

Gregor’s lawyer, Mario Gallucci, said their medical experts will testify that the child’s death was due to sepsis caused by pneumonia. He acknowledged during opening arguments Tuesday that viewing the tape would “horrify” the jury, but argued it had nothing to do with the death, which occurred about two weeks after the workout took place.

Prosecutors also noted the boy had contusions all over his body, and his heart and liver were lacerated. Gallucci said the bruises came from the treadmill and playing football.

Testimony continued in the trial this week and will resume next Tuesday. Besides the murder charge, Gregor also faces a child endangerment charge stemming from the treadmill video.