Italian prosecutors say 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,” but has been unable to provide a motive for a triple homicide that has shocked Italy. The minor, whose name is being withheld because of his age, is 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 murder has provoked a debate about the isolation of youths, following the pandemic and in an era dominated by social media.