LONDON — The chief judge hearing the appeal of William Labrador's murder conviction said Tuesday that it was clear that the prosecution's main witness was a "habitual liar" who arguably could say anything to extricate himself from a jam.

Other members of Judicial Committee of the Privy Council also did not mince words, saying that the trial judge should have cautioned jurors about a prison snitch's testimony and warned them that he might have had ulterior motives for testifying.

Based on that testimony, Labrador was sentenced to life in prison on the island of Tortola for the 2000 murder of fellow American tourist Lois McMillen, a 34-year old artist from Connecticut.

"It does seem to me that is absolutely crystal clear ... that a judge must give a warning of caution," Lord Steyhn said during the second day of a three-day hearing on the matter.

"What seems to be absent," Lord Hope of Craighead added, "is the comments of the judge ... Things weren't said that needed to be said."

The remarks by members of the Judicial Committee of the Privy Council, the highest court in England for appeals arising from the territories, seemed to give weight to the defense's argument that Labrador was scooped up by police in a classic rush to judgment and then wrongly convicted by a perverse justice system that placed value on the testimony of a career con man. That man, Jeffrey Plante, told authorities that Labrador confessed to drowning McMillen while the two shared a Tortola prison cell.

Victim Lois McMillen was staying at her parents' villa on Tortola

On Tuesday barrister James Dingemans argued in support of the prosecution, telling the committee members that Labrador's jury was fully apprised of Plante's long criminal record, lies he had told and the fact that he was facing extradition to Texas. They were also told that Plante faced fraud charges in the British Virgin Islands.

Even if the judge did not explicitly warn jurors, Dingemans argued, the jury was made well aware by the judge and all the lawyers involved that Labrador's conviction or acquittal hinged on Plante's believability and credibility.

"It was perfectly clear to the jury that they needed to approach this evidence with caution ... Everyone was aware that you had to approach this testimony with care," Dingemans argued.

He also argued that the outcome would not have been different had the trial judge explicitly warned jurors to treat Plante's testimony carefully. "The jury heard from Plante, and they heard from Mr. Labrador, and they came to their verdict ... It would be much nicer if I could come up here and say he said, 'Be cautious.' He didn't."

According to the defense, one of the best hopes for Labrador having his May 2001 conviction thrown out is a January ruling in different case by the same judges hearing his appeal. The judges ruled in a Jamaica case that convictions based on "cellmate confessions" are not "safe" unless the trial judge explicitly warns jurors to consider what the testifying inmate may have to gain.

Labrador, now 39, has been held by authorities in the British Virgin Islands ever since McMillen's battered body was found lying face up on the shore of Sir Francis Drake Channel on Jan. 15, 2000.

Labrador and three friends who knew McMillen were picked up for questioning within hours of the gruesome discovery. Investigators had no physical evidence or eyewitnesses.

Then Jeffrey Plante entered the picture. A convicted swindler and parole jumper from Texas, Plante was placed in Labrador's cell during the spring of 2000. As prosecutors scrambled to find anything of substance to show a magistrate at a fast-approaching probable cause hearing, Plante went to police to report that Labrador had confessed.

According to Plante's testimony, Labrador confided to his cellmate that he drowned McMillen by placing his foot on her neck during a violent argument over money.

Although the confession was vague, the trial judge ruled that it was enough to convict Labrador and that his case should go to the jury. The trial judge, however, said that Plante's testimony about prison conversations involving the other three men did not amount to enough to continue with prosecution and ordered them released before the defense portion of the trial.

Members of the defense team appeared to be lifted by the nature and tenor of questions the judges asked Dingemans during Tuesday's five-hour session. They are hoping that the judges will rule that any retrial with Plante at the center of it would not serve justice and quash the conviction altogether.

Senior Crown Counsel Terrence Williams, who prosecuted Labrador and is assisting Dingemans on the appeal, said as he did throughout the trial that is not authorized to make public statements about the case. "We're just doing our jobs," he said.

The Privy Council committee has yet to hear Dingemans' response to the appeal by Alexander Benedetto of New York. One of the original four defendants, Benedetto refused to return to Tortola to face a retrial after the Eastern Caribbean Court of Appeal ruled last year that the trial judge erred when he ruled there was insufficient evidence for the jury to determine whether Benedetto was also guilty of murder.

Plante testified that Benedetto and Labrador often argued in prison. At one point, Benedetto reminded Labrador that they borrowed $350,000 to start a business and that Labrador should "stop acting so pious" because "you are more guilty that I am."

Benedetto's defense lawyer, John Perry of London, argued Tuesday that the trial judge was correct to conclude that nothing Benedetto was quoted as saying could sustain a conviction for any crime. In court documents, prosecutors contend that the Privy Council committee should not even consider Benedetto's motion to have the acquittal reinstated as long as he remains a fugitive.

In addition to their concerns about the trial judge's jury instructions, the appellate judges also criticized prosecutors for suggesting during the trial that a court transcript could have been manufactured by the defense because it was not notarized. The transcript could have been authenticated with a single phone call, one of the judges noted.

The transcript dealt with Plante's 1995 testimony during a murder case in Hawaii. Authorities flew Plante from Texas to the Aloha State after he told prosecutors that he heard a murder defendant confess that he killed the victim during an argument over drugs.

Labrador's defense lawyers tried unsuccessfully to get the transcript admitted as evidence that Plante, if he was being truthful, had a history of hearing people confess murder. The Privy Council committee typically does not rule from the bench, although in rare cases they have. Decisions usually take about six weeks and are forwarded to the Queen in the form of a letter.