Chicago - With the US Supreme Court denying a last-minute appeal late on Thursday, Texas executed a convicted murderer who had claimed an ill-prepared attorney had botched his case and had relied on Wikipedia for research.Lawyers for TaiChin Preyor had made a last-ditch effort to save their client by asking the US Supreme Court to intervene just hours before he was scheduled to be put to death by lethal injection. But the high court let stand a lower court ruling in which judges expressed scepticism that further delays might change the outcome of Preyor's case. Preyor was executed soon after and declared dead at 21:22 local time (02:22 GMT), according to the Texas Department of Criminal Justice. Preyor, 46, was convicted of the drug-related murder of Jami Tackett in 2004, committed during the course of a burglary. Tacket was stabbed multiple times, and her throat was slashed - severing her trachea, jugular vein and carotid artery. Preyor was arrested still covered in blood on the grounds of the apartment complex where Tackett was killed. A jury rejected his claim of self-defence. The convict's attorneys had claimed his previous legal representation was woefully inadequate during the post-conviction phase of the trial.Lawyer 'ill equipped'They said his previous lawyer specialised in California real estate law, and was ill equipped for the task of appealing a death penalty case. They also discovered material in old case files that suggested the lawyer had relied on the Wikipedia website to research Texas death penalty law. "His attorneys and the judicial system itself have failed him at every turn," Preyor's attorneys wrote in their filing with the US Supreme Court. They argued Preyor's difficult childhood, including sexual and physical abuse, should have been considered at earlier phases of his case, which may have led to a life sentence instead of the death penalty. The 5th Circuit Court of Appeals rejected that argument, saying Preyor had "not made a substantial showing of the denial of a constitutional right"."He has not made a strong showing that he is likely to succeed on the merits" of his claim that additional evidence should be considered, the court wrote. In his brief last statement before execution, Preyor quoted the civil rights figure Coretta Scott King, saying: "Justice has never advanced by taking a life."Preyor is the fifth convict to face the death penalty this year in Texas. There are at least five others scheduled to be put to death this year in the state, according to the Death Penalty Information Centre.