South Korea’s Supreme Court upheld a 20-year prison sentence for a 15-year-old who killed his mother after she scolded him.

The court ruled on Oct. 31 that there were no errors in the lower court’s verdict, dismissing the defendant’s claims that he was mentally ill, according to media reports Tuesday.

The teenager was convicted of murdering his mother on October 1 last year, during the Chuseok holiday, at their residence in Cheongju, North Chungcheong Province. His mother was in her 40s.

Before the attack, the son reportedly became irritated by the noise coming from a playground near his apartment. He complained to his mother about the sound and she told him it was normal as children are playing during the holiday. When the son reported the noise to the police, his mother scolded him for being inconsiderate of others.

The son became infuriated and used a sharp weapon from the kitchen to stab his mother 28 times.

The victim was found by her husband, who immediately called emergency services, but she was pronounced dead at the hospital. Shortly after, the son was arrested near the apartment complex.

At the trial, the offender claimed that he had been suffering from mental illness, asserting that he was in a state of “mental incapacitation” at the time of the assault. Prosecutors refuted the claim with evidence from a psychiatric evaluation that concluded the defendant was mentally competent. Prosecutors sought the maximum 20-year prison term allowable for teenagers under the law.

In the initial trial, which was held as a jury trial – also known here as “Citizens’ Participation Trial” – jurors unanimously found the teenager guilty, rejecting his claims of mental incapacity. Eight of the nine jurors recommended 20 years imprisonment, while one suggested a term of 15 years with a minimum of seven years. Based on the jury's recommendation, the court handed down the 20-year prison sentence.

The appellate court also maintained the sentence, dismissing the defendant’s mental illness claims. It factored in the defendant’s lack of remorse and tendency to shift blame when making its decision.