"I had him come out and doing pushups because his arms were hurting, and when his arms started hurting, I made him do some squats and he did squats for a pretty long time," said Avant in the video.
He told detectives he was punishing the 5-year-old for getting in trouble at school, but not beating him.
"Is that normally (what) you make him do (to) discipline him?" asked the detective.
Avant said after letting Darell Jr. shower, he got worried.
"When I picked him up, his like, his, his head, just like, it was, it was like loose like, you know? You know, he not keeping his head, like, when I pick him up, it's just falling backward," Avant said.
Eventually, Avant told detectives he was done talking and wanted to leave.
He surrendered clothes later found to be stained with Darell Jr.'s blood, and his cellphone, with all internet history inside it.
Digital forensics expert James Montgomery told the jury that Avant was busy trying to figure out whether his son was dead and how to possibly revive him on the floor of their apartment.
"Video how to check an infant's pulse for CPR, once again, from the e-How website," said Montgomery.
Prosecutors claim the delay cost Darell Jr. his life.