
Provincial Police Region 3 deputy chief Pol Maj General Boonchan Nuansai said Jiran Pansuan, a former boxer, was arrested in Bangkok on Wednesday and taken to Nakhon Ratchasima for interrogation on Thursday.
Jiran told police that he was with the boy alone in their apartment when the boy slipped, fell and began crying.
He said he was sleepy after drinking with friends the previous night so he hit the baby in the stomach several times until the boy went silent and unconscious.
Jiran took the boy to hospital claiming he had drowned but the toddler died from a ruptured liver, police say. The boy's bruised body led police to identify Jiran as the prime suspect and an arrest warrant was issued the following day.
Jiran said he was sorry for what he did and would become ordained as monk to make merits for the young victim.