Bonne Terre, Missouri - A Missouri man who sexually attacked a 19-year-old woman before tying her to a cemetery tree and killing her was executed Tuesday after the US Supreme Court and the governor declined to intervene.David Zink, 55, was put to death at a state prison near Bonne Terre, south of St. Louis, hours after the nation's high court rebuffed his last appeals and Governor Jay Nixon rejected his clemency request. Corrections Department spokesperson Mike O'Connell said the lethal injection began at 19:33 and Zink was pronounced dead at 19:41.Zink began breathing haltingly shortly after the injection began, O'Connell said. His right hand twitched several times before Zink eventually became motionless.Zink was convicted and recommended for a death sentence in the 2001 killing of Amanda Morton. Authorities said Zink abducted her after hitting her car from behind on a highway exit ramp 1.6km from her Strafford home. Morton was driving home after visiting a friend.'Threat to my freedom'Just months before the slaying, Zink had been released from a Texas prison after serving 20 years on rape, abduction and escape charges. Fearing that his drunken fender-bender with Morton could violate his parole and send him back to prison, Zink abducted Morton, taking her to a motel."If I think that you're going to pose a threat to my freedom, it is set in my mind I want to eliminate you," Zink said in his videotaped confession.The motel's manager later saw a televised news report about Morton's disappearance, recognised her as the woman who had checked in with Zink, and gave investigators Zink's name and license plate number from motel registration.Zink, after being arrested at his parents' home, led authorities to Morton's buried body in a cemetery, confessing matter-of-factly and at times laughing on videotape that he had tied her to a tree there and told her to look up. When the bewildered Morton begrudgingly glanced skyward, Zink said, he snapped her neck, choked her with his hands and a rope, and stuffed her mouth with mud and leaves.Broken ribsWorried that Morton might regain consciousness, Zink admitted, he used a knife to sever her spinal cord at the neck.An autopsy showed Morton had eight broken ribs and 50 to 100 blunt-force injuries. She also had been sexually assaulted.Zink had appealed to stop his execution. A three-judge panel of the 8th US Circuit Court of Appeals on Tuesday declined, without comment, his claims that the death penalty was unconstitutional. On Monday, the St Louis-based court had rejected his challenge of the drug process used during lethal injections.His appellate attorneys did not accept requests by The Associated Press for interviews this week.Messages left Monday with Morton's mother and sister were not returned.Zink became the fifth man executed this year in Missouri and the 17th since November 2013. Only Texas has executed more inmates over that span.