Errol Hillary, the man accused of gunning down a popular Mount Vernon nightclub owner on Christmas Day and wounding five other men, pleaded not guilty Thursday, according to Westchester County District Attorney Anthony A. Scarpino, Jr. The Bronx resident, 41, who did not speak during the arraignment before Judge Barry Warhit in Westchester County Court, is accused of killing O’Neil Bandoo and injuring five others following an argument around 4:30 a.m., Dec. 25, 2016, inside the Mansion at 4 N. Third Ave. He is charged with second-degree murder, criminal possession of a weapon, five counts of second-degree attempted murder, four counts of assault and one count of second-degree assault, all felonies, Scarpino said.