An inmate who was killed in a 'horror movie-style' botched execution last year chatted with prison guards and even suggested a vein in his leg for his lethal injection, new documents have revealed. Clayton Lockett, who shot and buried alive Stephanie Neiman, 19, in 1999, was scheduled to be put to death by an untested cocktail of three drugs, including  midazolam, in Oklahoma on April 29. But after medical officials repeatedly failed to set up an intravenous line - ultimately, pumping the drugs into his femoral artery, causing them to leak into his tissue - he took  43 minutes to die. Now, newly-released transcripts of interviews with officials inside the state's death chamber have revealed grisly details of the moments leading up to the 'bloody mess' that was Lockett's death. Scroll down for video . Murder: Clayton Lockett (left), who shot and buried alive Stephanie Neiman (right), 19, in 1999, chatted with prison guards and even suggested a vein in his leg for his lethal injection, new documents have revealed . The botched killing led to a temporary moratorium on executions in Oklahoma while the U.S. Supreme Court considers whether the state's three-drug method is constitutionally humane. The interviews, which are among 5,000 pages of documents unveiled by the Oklahoma Department of Public Safety, show Lockett causally chatted with the paramedic who was inserting his IV line. He told the paramedic his arm was scarred from previous drug use, but  there still was a viable vein in it . 'And he said if you will go right above the scars, I have a good vein,' the paramedic said. Although the official took Lockett's advice and successfully inserted the needle, they did not have the right kind of tape to hold the line in place, so it came loose, according to the interview transcripts. Lockett, a former intravenous crystal meth user who had dehydrated himself for three hours for the execution, then suggested that officials insert the needle through his leg instead, NBC reported. 'He said, 'I've got a vein in my leg, my right leg,' the medic recalled in an interview. 'And I said, "Well, I don't like to do those because they cause a lot of clots". 'He said,"Does it really matter?"' Botchedi njection: Lockett was scheduled to be put to death at Oklahoma state prison (above)) by an untested cocktail of three drugs, including the sedative midazolam, on April 29. But after medical officials failed to set up his intravenous line - ultimately, pumping the drugs into his femoral artery - he took a huge 43 minutes to die . Lethal: Now, newly-released transcripts of interviews with officials inside the death chamber have revealed gthe moments leading up to Lockett's death. Above, one of the drugs used in the execution, midazolam . Officials ultimately chose to put the IV into Lockett's femoral vein through his groin, using a 1.25in needle that appeared to be too short for the procedure - the recommended length was 2.5in. 'Well, we'll just have to make it work,' the doctor told the concerned medic,  the transcripts state. By the time the second drug, a paralytic, was pumped into Lockett, it was clear something was wrong. The inmate, who was apparently 'very talkative until they raised the curtain' in his execution and then he shut up', had been declared unconscious, but he suddenly started writing in agony. 'One of the executioners said, "He's trying to get up off the table" and I thought, "What?"' said the medic, who has not been identified. 'The warden was very upset. Nobody wants a prisoner in an execution situation to suffer.' Lockett, 38, also began clenching his teeth and groaning loudly, prompting officials to try unsuccessfully to stop the execution. More than 43 minutes after the killing began, Lockett died. Death row inmates typically take just 10 minutes to die from a lethal injection. The cocktail of drugs that Lockett had been injected with had not been previously used in the United States. Other witness interviews, unveiled to the Associated Press after The Tulsa World successfully filed a lawsuit against authorities, also laid bare the scale of the fiasco surrounding Lockett's execution. Some witnesses said the killing resembled a scene from a 'horror movie'. Meanwhile, prison warden Anita Trammel described it as a 'bloody mess' as the inmate bucked up from the gurney when he was meant to be unconscious, the New York Times reported. Halted: After Lockett's execution went awry, Gov Mary Fallin ordered a halt to the second scheduled killing of Charles Warner (left), who sexually assaulted and killed 11-month-old baby Adrianna Waller (right) in 1997 . DPS released a 32-page summary of its investigation in September, which blamed most of the execution's problems on a failed single IV line in Lockett's groin. However, the agency did not release the documents connected to its probe until after The Tulsa World's lawsuit. The investigation revealed a failed line caused the drugs to be administered locally instead of into Lockett's blood, but the doctor overseeing the execution did not notice a problem with the site. This is because Lockett's lower body was covered with a sheet, the transcripts state. The documents also reveal that the newly hired executive director of the Department of Corrections, Robert Patton, was concerned about his lack of involvement in the execution preparations. Prison warden: Anita Trammel (pictured) described Lockett's execution as a 'bloody mess' as the inmate bucked up and groaned on the gurney . Patton told investigators he didn't even know the agency had acquired the drugs for the execution until he learned it from the media. 'I found out that they had found a pharmacist and the drugs, uh through a news report,' Patton said, according to a transcript of his interview. The testimony of Patton and others involved in the execution suggest there was nervousness and unease with two executions scheduled on the same night using a new three-drug formula that hadn't been used in Oklahoma before. 'These were particularly concerning to me,' Patton said. 'A new protocol, one I was not familiar with really.' Indeed, the unidentified paramedic recalled: 'There was an air of urgency there. The "quick quick, got to get it done, got to get it done and got to make sure that everything is done right".' After Lockett's execution went awry, Gov. Mary Fallin ordered a halt to the second scheduled execution of Charles Warner, who raped and murdered an 11-month-old girl in 1997. Warner was executed nearly nine months later, on Janyary 15, using the same three drugs in Lockett's execution, but with a five-fold increase the amount of the first drug, midazolam. Since Warner's execution, the U.S. Supreme Court has agreed to consider a challenge to the new three-drug method from a group of Oklahoma death row inmates who claim the sedative won't properly render them unconscious before the second and third drugs are administered. A legal brief in that case filed this week by 16 pharmacology professors at US universities states that midazolam is incapable of rendering an inmate unconscious and is an inappropriate first drug to use. The court is scheduled to hear arguments in the case on April 29. Patton and other state officials have publicly acknowledged midazolam is not the preferred drug for lethal injection, but one that was selected when other more effective, drugs became unavailable. because manufacturers refused to sell them to states for use in executions. All execution officials' names and identifying information were redacted from the DPS records.
Clayton Lockett, 38, shot and buried alive Stephanie Neiman, 19, in 1999 . Prisoner was killed in 'horror movie-style' botched execution last spring . New documents have revealed  he chatted with Oklahoma prison guards . Even suggested a vein for lethal injection after medic could not find one . Untested cocktail of 3 drugs ultimately leaked into Lockett's body tissue . Execution described as a 'bloody mess'; prisoner took 43 minutes to die .