The security guard who is accused of firing his semi-automatic gun into a crowd of people in Columbus Park just as the bars and clubs were closing pleaded not guilty to the charges against him yesterday in state Superior Court in Stamford. Dayron Wills, 22, of 300 Tresser Blvd., pleaded not guilty to five charges of first-degree assault and single counts of unlawful discharge of a weapon, reckless endangerment and marijuana possession. Police say that after they apprehended Wills a short time after the shootings, which were caught on video by a bystander, he admitted to firing his gun into the crowd, explaining that a man had struck him with his fist, and so he pulled out his gun. Because of his earlier gunshot injury, Seeger said Wills was off balance and can't run anywhere. In addition to the video recordings of the shooting, Stamford police also recovered 10 shell casings from a two-block area which they have said they are certain came from Wills' .40-caliber handgun.