WASHINGTON (Reuters) - Conservative new U.S. Supreme Court Justice Brett Kavanaugh on Tuesday joined liberal colleagues in raising concerns about Missouri’s plan to use lethal injection to execute a murderer with a rare medical condition.

FILE PHOTO: Death row inmate Russell Bucklew is shown in this Missouri Department of Corrections photo taken on February 9, 2014. REUTERS/Missouri Department of Corrections/Handout via Reuters

Lawyers for Russell Bucklew, 50, have argued that because of a congenital condition called cavernous hemangioma that leaves him with blood-filled tumours on his body, the lethal injection could cause undue agony in violation of the U.S. Constitution’s prohibition on cruel and unusual punishment.

Based on the one-hour oral argument, it is not clear how the court will rule in Bucklew’s case but Kavanaugh’s comments in his first death penalty-related oral argument since joining the court last month suggest he could potentially break with fellow conservatives.

If he joins the court’s four liberals, the court could issue a narrow decision sending the case back to lower courts to determine whether the state can accommodate Bucklew’s medical issues.

Kavanaugh, a conservative appeals court judge, was appointed by President Donald Trump and joined the court last month after a fierce Senate confirmation battle.

During the argument he appeared to question Supreme Court precedent that requires inmates to come up with an alternative method of execution if they think the state’s preferred method is too painful.

“So you’re saying that even if the method imposes gruesome, brutal pain, you can still go forward?” Kavanaugh asked the state’s lawyer, John Sauer. “Is there any limit on that?”

His comments seemed to address two previous rulings in which the court has declined to invalidate lethal injection procedures but said inmates can propose less painful alternatives.

In Missouri, execution is authorized using either injection or gas but the state in practice uses only lethal injection. Bucklew, whose appeal is neither contesting his guilt nor seeking to avoid execution, has suggested being put to death by gas. Lawyers for the state say that although lethal gas is authorized, it has never been used and there are no protocols for it.

The high court on March 20 blocked Bucklew’s execution on a 5-4 vote, with four of the court’s five conservative justices voting to deny the request. The conservative justice who voted with the court’s four liberals to grant the stay, Anthony Kennedy, has since retired and was replaced by Kavanaugh.

Bucklew was convicted of the 1996 murder in southeastern Missouri of Michael Sanders, who was living with Bucklew’s former girlfriend Stephanie Ray at the time. Bucklew fatally shot Sanders at his trailer home, kidnapped and raped Ray, shot at Sanders’ 6-year-old son and wounded a police officer before being apprehended, according to court papers.

Bucklew’s condition has caused large, blood-filled tumours to grow on his face, head, neck and throat, according to court papers.

A ruling is due by the end of June.