The suspected Highland Park mass shooter once tried to commit suicide, then threatened to “kill everyone’’ in his home while hoarding a huge stash of knives months later — yet was still able to legally buy rifles and pistols afterward, officials acknowledged Tuesday. Authorities revealed that Robert E. “Bobby” Crimo III, 21, had legally purchased at least five firearms — including the AR-15-style rifle he allegedly used in Monday’s massacre — after his two troubling interactions with law enforcement in 2019. Officials said cops were called to Crimo’s home in April 2019 after receiving a report that he had attempted suicide a week earlier. Officers spoke to Crimo and his parents, but the matter was handled by mental-health professionals at time, said Lake County Major Crime Task Force spokesman Christopher Covelli at a news conference. “There was no law-enforcement action to be taken. It was a mental-health issue handled by those professionals,” Covelli said.