HELENA — A trial to determine the legality of an execution drug concluded Thursday after attorneys for Montana’s two death-row inmates disputed the credibility of the state’s key medical witness.

District Court Judge Jeffrey Sherlock decided to strike a portion of testimony from a pharmacist the state brought in to defend its plan to use pentobarbital in lethal injections. The judge must now decide whether that drug would adequately sedate a person being put to death or cause undue pain and suffering.

Attorneys for convicted killers Ronald Allen Smith and William Gollehon sharply criticized Roswell Lee Evans, the dean of Auburn University’s pharmacy school, for making conflicting declarations during the seven-year-old case.

Evans said in court this week that pentobarbital is by definition an ultra-fast acting drug, as state law requires. He said it takes effect in less than one minute.

That contradicted a statement Evans made in a deposition that the drug merely could be ultra fast-acting.

“Whether it’s a big deal or a little deal, it’s different from what was previously stated,” Sherlock said before deciding to only consider the earlier account.

State attorneys on Wednesday challenged the inmates’ medical expert, Columbia University Medical Center anesthesiologist Dr. Mark Heath.

Assistant Attorney General Pam Collins directed attention to the fact that Heath has not witnessed any executions using pentobarbital and, despite his claims, could not name any cases in which a prisoner continued to speak, breathe and move after the drug was administered.

Jim Taylor, an ACLU attorney for the inmates, told Sherlock that Evans is not a medical doctor, has never administered anesthesia and has never witnessed an execution. Taylor brought to light a statement Evans made in 2012 that pentobarbital’s onset is three to four minutes — significantly longer than one minute as he said this week.

“It was a rough guess, maybe an educated guess, but a rough guess,” Evans said Thursday of his 2012 statement.

Taylor pointed to another lethal-injection case in 2013, in which Evans reaffirmed that he believed pentobarbital to take three to four minutes to take effect. “Did you understand that people’s lives literally depended on your testimony?” Taylor said.

Collins said Evans made those statements when his expertise was sought on midazolam, a different sedative that the U.S. Supreme Court upheld for use in capital punishment in June.

Evans said in a February deposition that he has participated as an expert witness in 35 lethal-injection court cases, including the high-profile midazolam case.

Smith and Gollehon were sentenced to death after being convicted of murder in 1983 and 1992, respectively. Their executions have been stayed for the duration of the case.