The 32-year-old Nui, who has no last name, was given two life sentences previously for killing two girls aged six and four.
The verdict was delivered at the Ratchadapisek Criminal Court Tuesday. The convict reportedly confessed to raping and murdering the boy during police interrogation, and even provided a map to where the boy’s corpse was hidden, but then denied the crime in court.
The court however found him guilty and initially gave him a death sentence for the boy’s murder as well as several years in prison for other counts before commuting all sentences to life in prison.