NEW YORK -- A homeless ex-con accused of beating and sexually assaulting a 73-year-old birdwatcher in Central Park randomly groped two more women near the park before his capture, authorities said Tuesday.Prosecutors announced the additional allegations against David Albert Mitchell at an arraignment Tuesday in state court in Manhattan. They also accused him of threatening to spit on and punch police officers following his arrest.In addition to first-degree rape, the jailed Mitchell pleaded not guilty Tuesday to lesser charges of forcible touching and sex abuse involving the two other women. They credited the original victim with helping identify the alleged attacker, described as a drifter from West Virginia with a violent past."We want to thank the victim for her courage and for her assistance in the investigation," District Attorney Cyrus R. Vance Jr. said in a statement.There was no immediate response to a phone message left Tuesday with an attorney representing Mitchell.Prosecutors have portrayed the broad-daylight assault of the 73-year-old as an act of vengeance.It occurred on Sept. 12, about a week after she photographed Mitchell exposing himself to create "evidence of his lewd act," prosecutors said. Around 11:30 a.m., he allegedly approached her in the park and asked, "Do you remember me?" before beating and raping her, then stealing her camera bag.Later that afternoon, Mitchell accosted two more women on nearby streets on Manhattan's Upper West Side, prosecutors said, without going into greater detail.Once New York Police Department officers grabbed him, Mitchell claimed he was recently sprung from prison and homeless, and that he carried condoms for sex with women in Central Park, prosecutors said in court papers. He also said he found the camera case he had in his possession "on a bench by the trash," the papers said.Mitchell also pleaded not guilty Tuesday to separate weapons and menacing charges alleging he pulled a knife on a man on Aug. 20 during a confrontation in Central Park.Records show that Mitchell was once sentenced to eight years in prison after pleading guilty in an abduction case. Authorities say he also had been acquitted of murder charges in his native West Virginia, and was eyed as a potential suspect in another slaying.In 1989, when Mitchell was 18, police in McDowell County arrested him and charged him with murder in connection with the sexual assault and fatal beating of Annie Parks, 86, at her home in Jenkinjones.At the time, West Virginia State Police said they believed robbery was the motive, even though nothing was taken from Parks' home. They said Mitchell killed her by hitting her with a blunt object.Sid Bell, now McDowell County's prosecuting attorney, was in private practice at the time and was appointed to represent Mitchell, Bell told the Gazette last month.Mitchell was willing to accept a plea deal and plead guilty to murder, Bell said, but prosecutors rejected the plea and the case went to trial. A jury then acquitted Mitchell of the murder charge, Bell said.Just a few months later, Mitchell was arrested again in McDowell County. Bell said Mitchell was accused of breaking into the home of a woman in her late 70s, raping her and stealing a firearm.Bell was again appointed to represent Mitchell in court."When I was appointed to represent him [the second time], he asked me to get him the best possible plea deal," Bell told the Gazette. Prosecutors agreed to drop a sexual assault charge if Mitchell pleaded guilty to first-degree robbery, which he did, Bell said.Mitchell was sentenced to 10 years in prison. He served about eight years before he was released on parole, Bell said.