Hearing his first arguments in a death penalty case, Supreme Court Justice Brett Kavanaugh seemed open Tuesday to the arguments of a Missouri inmate who says his rare medical condition could result in severe pain if he is executed by lethal injection.

Hearing his first arguments in a death penalty case, Supreme Court Justice Brett Kavanaugh seemed open Tuesday to the arguments of a Missouri inmate who says his rare medical condition could result in severe pain if he is executed by lethal injection.

The court's newest justice could hold the key vote in Russell Bucklew's case. That's because his eight colleagues split 4 to 4 earlier this year over whether to allow Bucklew's execution to proceed. Justice Anthony Kennedy provided the fifth vote to spare Bucklew. Kavanaugh replaced Kennedy, who retired in July.

Bucklew, on death row for a 1996 murder, has said that a tumor in his throat is likely to burst during the lethal injection procedure, causing him to choke on his own blood.

Among the questions Kavanaugh wanted answered was whether Bucklew will be lying flat during the execution, which Bucklew's attorneys have said could be problematic. Kavanaugh, who heard no death penalty cases in his 12 years as an appeals court judge, also asked about the limits on pain associated with an execution.

The justice also aimed all his questions at the lawyer representing Missouri, which can be a sign at the Supreme Court that a justice is inclined to vote for the other side.

But Bucklew is up against Supreme Court precedent in trying to get the justices to agree with him. The court has previously ruled that inmates challenging a method of execution have to show that there's an alternative that is likely to be less painful. Bucklew has proposed that Missouri execute him by having him breathe pure nitrogen gas through a mask instead of by injecting him with a lethal dose of pentobarbital.

Bucklew says it is likely he would essentially suffocate for several minutes if he is given a drug injection. He says if the state uses nitrogen gas, he'd become unconscious within 20 to 30 seconds.

Missouri law still provides for the option of lethal gas, but the state has not used the method since 1965 and it no longer has an operational gas chamber. Missouri says no state has ever carried out an execution as Bucklew suggests, calling his proposal vague and untested. And the state says Bucklew would not suffer severe pain during a lethal injection because pentobarbital would make him unconscious within 20 to 30 seconds, likely sooner.

Bucklew is on death row for the 1996 murder of Michael Sanders, who was living with Bucklew's former girlfriend. After entering a trailer where the two were living with their children, Bucklew fatally shot Sanders and forced the woman into a stolen car, later putting a gun to her head and raping her. Bucklew was arrested after a car chase and shootout with police. He later escaped from jail and attacked his ex-girlfriend's mother and the woman's fiance with a hammer and a knife before being captured again.

A decision in Bucklew v. Precythe, 17-8151, is expected by spring.