Corey Johnson seemed almost happy as he fatally stabbed a 13-year-old boy and attacked two other people during a March 2018 sleepover in Palm Beach Gardens, one of his victims told jurors Wednesday. The testimony came on the first day of Johnson’s trial on murder and attempted murder charges. Defense attorneys said Johnson was insane at the time of the attacks, and that his interest in Islam drew him toward violent videos touting the Islamic State group. Dane Bancroft, one of Johnson’s victims, said he’d known Johnson for years and had never seen him injure anyone before that morning.