A convicted murder with a rare medical condition was set to be executed on Tuesday by lethal injection in Missouri despite his assertions that this method of capital punishment will cause him terrible suffering.Russell Bucklew was sentenced to death after being found guilty of killing his ex-girlfriend's new boyfriend in 1996, then abducting and raping her.Bucklew, 51, suffers from a disorder called cavernous hemangioma, a blood vessel condition that hinders his breathing. For the past year he has been using a tracheotomy tube.His lawyers say his execution could be horrific if done by lethal injection."His face is swollen by the bulging, blood-filled tumors in his face, head and throat. These unstable tumors are highly likely to hemorrhage during the stress of the execution, causing Russell to cough and choke on his own blood," the lawyers wrote in a petition asking Missouri's governor to commute the sentence and have Bucklew serve a life term instead.Governor Mike Parson, a Republican who supports the death penalty, turned down the request Tuesday morning.So Bucklew is scheduled to receive a lethal injection at 0100 GMT and become the 17th death row inmate put to death in the US this year.Authorities in Missouri had twice set dates for the man's execution, in 2014 and 2018. Both times the US Supreme Court ordered last minute stays, before eventually ruling on the substance of the case.Former prison wardens came out in favor of Bucklew's request, saying they wanted to spare their colleagues the torment of a messy, botched execution in this case."Participating in executions places a tremendous weight on the shoulders of the execution team," they said in an amicus brief to the court."When as here, an execution is unlikely to go smoothly, and is likely to result in unnecessary pain and suffering, the burden of participation becomes unbearable," the letter says.In April, the US Supreme Court rejected arguments over how cruel it would be to execute this man by lethal injection."The Eighth Amendment does not guarantee a prisoner a painless death," the majority judges said in a 5-4 ruling. The amendment, they said, just bans adding more suffering to that needed to carry out an execution, they said.The court's four liberal judges disagreed."Executing Bucklew by lethal injection risks subjecting him to constitutionally impermissible suffering," Justice Stephen Breyer wrote on behalf of the liberals.