The trial of a man accused of killing his 6-year-old son is now underway in Ocean County. Christopher Gregor is accused of killing Corey Micciolo in April 2021.

This case will focus on two key dates in 2021 - March 20 - the day Gregor allegedly injured his son by placing him on a treadmill - and April 2 - the day the boy died.

Both sides had the opportunity on Tuesday to speak to the 16 seated jurors about what they will hear over the next month and a half. And the video of the alleged treadmill abuse was shown to the public for the first time.

Security video from March 20, 2021, captured Gregor allegedly placing the boy on a treadmill over and over again as he struggled to maintain his footing. The gym was located inside the Atlantic Heights apartment complex in Barnegat where Gregor lived. Corey is seen falling off the treadmill half a dozen times. Prosecutors say this led to bruising on the boy’s body.

Before the video was shown, Assistant Prosecutor Jamie Schron spent 10 minutes presenting the case against Gregor to the nine women and seven men making up the jury and alternates. Corey died on April 2, 2021, in an Ocean County hospital. Gregor faces charges of child endangerment and murder.

"This defendant had carried Corey's nearly limp body into Southern Ocean Medical Center. He reported that Corey was sleepy and throwing up. Corey was admitted quickly and he was brought to Room 6 in the emergency department. He was intubated, he coded again. He lost his pulse and by 5:03 p.m. Corey was pronounced dead," said Schron.

Defense attorney Mario Gallucci said the boy did not die from injuries sustained by his dad, rather he died of a sepsis infection. He also warned the jury about the treadmill incident.

"You're not gonna like him. And I don't care that you don't like him. You'll be horrified and mortified - evidence you will see of Corey's death had nothing to do with that treadmill," said Gallucci.

Corey's mother Bre Micciolo took the stand as the first witness called by the prosecution and described custody issues. She testified that she noticed bruises on Corey's body days before he died, allegedly from the treadmill incident. Under direct examination, she said she worried Corey would die.

Testimony is set to resume Wednesday at 9 a.m.