ROAD TOWN, British Virgin Islands —The primary prosecution witness in the trial of four Americans charged with killing Lois McMillen last year took the stand just before noon Tuesday and began describing how he met and befriended the suspects in prison.

Jeffrey Plante, a 59-year-old Texan with a long conviction record, has lost weight and grown a gray beard since testifying last summer that defendant William Labrador admitted drowning the 34-year-old Connecticut artist after a heated argument over money. Plante testified for just 30 minutes before the lunch break Tuesday and prosecutor Terrence Williams clearly wanted the nine-member jury, which has been sitting here since April 2, to know that his star witness is not an upstanding citizen.

In fact, Williams established within the first five minutes of Plante's testimony that he was convicted of theft in Texas in 1985 and is currently being held at a police station on Tortola while he awaits prosecution for allegedly passing bad checks.

Wearing tinted glasses, a blue suit and a black tie with a white crisscross design, Plante bowed his head as he testified. Asked to identify the defendants, Plante looked up, swung his body around and pointed as he said, "That's William Labrador, Michael Spicer, Alexander Benedetto and Evan George."

Plante then went on to tell the jury about hearing loud arguments inside Her Majesty's Prison between Labrador and Benedetto.

"They were constantly arguing and raising a fuss. From what I heard, Mr. Labrador was telling Mr. Benedetto to keep his mouth shut," Plante said on the stand.

Benedetto and Labrador were separated, and Plante was then moved into a cell with Labrador, according to the testimony. "We were fellow Americans who discussed a lot of things, and we obviously got to know each other pretty well," Plante said. "We talked a great deal and developed a trust."

Plante's testimony so far mirrors almost exactly the deposition he gave at a pretrial hearing last summer. He was expected to tell the jury later Tuesday about a conversation he claims he had with Labrador several days before Good Friday in 2000. At the time, according to Plante's pretrial testimony, Labrador confided that he drowned McMillen by holding her neck down under the water in Sir Francis Drake Channel after forcing her to pull her rental car to the side of the road.

Barbara Labrador, of Southampton, N.Y., who maintains that her son never made such statements, said she counted no fewer than six lies by Plante already. She declined to elaborate. Michael Griffith, a New York attorney assisting the defense, said destroying Plante's credibility will not be a problem when the defense gets its turn to question the witness.

"This guy Plante isn't just going to fall on his sword. When the defense gets done with him, he's going to fall into the nuclear reactor in Chernobyl, "Griffith said.