The video lasting more than four minutes shows Nam continuously beating, slapping, kicking and yelling at the boy, who had no clothes on.
As the five-year-old boy kept screaming: "Please don’t beat me dad," Nam did not stop and threatened to throw him out of the house.
Halfway through the video, the boy managed to stand up and wanted to go inside "to save mom" but Nam did not allow that and beat him even harder.
A woman who seemed to be the boy's mother also appeared in the video but she kept hiding and it was not until the end of the video that she rushed to protect the boy.
At that moment, Nam attacked both the woman and boy, saying: "Either I leave you or you send him back to your parents."
It seems like a person in the attic of the apartment, in Thuan An Town, captured the whole scene and posted it online.
As Thuan An Police probed the case, they identified the man as Nguyen Hoai Nam and the location a rented apartment in the town’s Binh Chuan Ward.
At the police station, Nam admitted to his behavior.
He said he has been living with the boy’s mother and is not the father.
Police are looking into the case.