The police here said Monday that they had found “no substantive basis” to support a Rolling Stone magazine article depicting a horrific gang rape at a University of Virginia fraternity house and that a four-month review had identified serious discrepancies in the account by a woman identified as Jackie, who refused to cooperate with their investigation. After a review of records and roughly 70 interviews, Police Chief Timothy J. Longo Sr. said at a crowded news conference here, his investigators found “no evidence” that a party even took place at the Phi Kappa Psi fraternity on Sept. 28, 2012, when the rape was said to have occurred. Instead, he said, there was a formal that night at the house’s sister sorority, making it highly unlikely that the fraternity would have had a party on the same night.