The loss of a witness on behalf of the state of Montana could have an impact on Canadian Ronald Smith's attempt to avoid death by lethal injection.

A hearing is scheduled for next July on whether new drugs being proposed by the state comply with language in execution protocol requiring an "ultra-fast-acting barbiturate."

But an expert who Montana was going to use in its argument has withdrawn his services and the state has been unable to find a replacement.

Lawyer Ron Waterman of the American Civil Liberties Union says it may be possible to get the court to consider issuing a ruling based on the evidence it already has.

Mark Dershwitz, an anesthesiology professor at the University of Massachusetts Medical School, has provided expert opinions about lethal injection for more than 20 states and the federal government.

"He's one of the only persons willing to do that ... (but) he is no longer willing to testify. He is pulling himself out. Since June they have not been able to find anybody who is willing to step forward," Waterman, lead lawyer for the civil liberties union, told The Canadian Press on Friday.

Waterman said his group is researching whether there is room to ask that the judge make a ruling without another hearing.

'It hurts their case tremendously'

"The state had filed an affidavit. The person in the affidavit they had filed is no longer an expert. So the question now comes what are the consequences of that? asked Waterman.

"We may be able to ask the court to review our motion for a summary judgment. It hurts their case tremendously."

Smith, 56, was convicted in 1983 for shooting Harvey Madman Jr. and Thomas Running Rabbit while he was high on drugs and alcohol near East Glacier, Mont.

He refused a plea deal that would have seen him avoid death row and instead pleaded guilty. He asked for and was given a death sentence.

But Smith had a change of heart and has been fighting to avoid execution ever since.

The civil liberties union filed a lawsuit in 2008 on behalf of Smith and another death-row inmate in Montana.

It argued that the lethal injections the state was using were cruel and unusual punishment and violated the right to human dignity.

District court Judge Jeffery Sherlock ruled in 2012 that the injections were unconstitutional. He also pointed to a lack of training for individuals who administer the drugs and to a discrepancy over whether two or three drugs should be used.

But last May, the judge ordered a trial to determine whether new drugs would satisfy requirements.