15-year-old boy kills grandmother, stabs mom in Long Island home: cops

A 15-year-old boy killed his grandmother and stabbed his mother — who was helped by a passing driver after she fled the gory scene in their Long Island home Monday night, according to police.The teen’s mother, 36-year-old Vanessa Chendemi, ran out of their Selden home after she’d been stabbed by her son around 9:45 p.m., flagging down a motorist and calling 911 once she was in their vehicle, according to the Suffolk County Police Department.When cops arrived at the residence on 802 Old Town Road, they found the teen’s grandmother, 56-year-old Concetta Chendemi, with multiple stab wounds.She was pronounced dead at the scene.Vanessa Chendemi was taken to an area hospital in stable condition. The teen, who has not been identified by authorities due to his age, fled the scene after the stabbings.Cops tracked him down and took him into custody less than half a mile away near Dare Road and Buckskin Lane in Selden around 11:22 p.m.He is charged with second-degree murder and attempted murder and is scheduled to be arraigned at First District Court in Central Islip Tuesday....