MILAN (AP) — A 17-year-old high school student, who confessed to stabbing to death his 12-year-old brother and parents, had been suffering a general sense of “malaise,” Italian prosecutors said Monday, adding that he has been unable to provide a motive for a triple homicide that has shocked Italy.

The minor, whose name was being withheld because of his age, was being held on suspicion of murder with aggravating circumstances including premeditation.

The stabbings happened around 2 a.m. Sunday morning in a Milan suburb following a family gathering for the father’s 51st birthday.

The youth took a knife from the kitchen and first entered the room he shared with the younger brother and stabbed him, according to prosecutors. When his mother came to investigate, he stabbed her and then the father, as he attempted to give aid to the younger son.

All three suffered multiple stab wounds to the throat and neck, said Sabrina Ditaranto, a prosecutor handling youth offenders.

The suspect called the police, initially claiming to have killed only the father in self-defense, accusing him of having killed the mother and brother. He eventually confessed to all three murders.

“From a judicial point of view, we don’t have a motive,’’ Ditaranto told a news conference.

“He does not give a logical and coherent explanation for what happened,’’ she added, saying he had referred to a general sense of “malaise,” that was “his own” and not related to any family issues.

The murder has provoked a debate about the isolation of youths, following the pandemic and in an era dominated by social media. Ditaranto said they scoured the suspect’s use of social media and music, and no clear picture has emerged, beyond his description of feeling isolated.

It also comes after another stabbing death of a 33-year-old woman out on an evening walk near the northern city of Bergamo on July 30, in an apparently random crime. Prosecutors on Monday confirmed the detention of Moussa Sangare, 30, a one-time aspiring singer, arrested nearly a month after the murder who told investigators that he had chosen his victim randomly.