BANGOR — A prison inmate who described himself as a friend of one of the two men on trial for the murder of three people refused to testify Monday at the Penobscot Judicial Center. He said he was afraid of retribution if he told the court what he knew.

Nicholas Sexton, 33, of Warwick, Rhode Island, and Randall “Ricky” Daluz, 36, of Brockton, Massachusetts, are both charged with three counts of murder and one count of arson in the August 2012 crime. Both have pleaded not guilty.

Alfred Lanpher, 44, said Sexton was his friend and gave him a nod when he entered the courtroom. When Assistant Attorney General Lisa Marchese, who is prosecuting the case with Assistant Attorney General Deb Cashman, asked him questions about the murder case, Lanpher declined to answer.

“I already advised this lawyer here that I’m not going to testify,” Lanpher said, indicating attorney William Bart, who was sitting beside him in the courtroom.

Bart did not address the court.

“I don’t want to testify here because I am going to spend the next three years in jail,” Lanpher later said on the stand.

Lanpher of Mount Desert Island is serving a 4½-year sentence at the Maine State Prison in Warren for assaulting a Southwest Harbor police officer in 2012.

Marchese asked if he was afraid of retribution for being “a rat.” Lanpher replied, “yeah.”

Lanpher did say on the stand that he was using illegal drugs around the time of the three murders and when he testified in front of the Penobscot County grand jury shortly afterward.

Marchese asked the judge to force Lanpher to testify or to allow the prosecution to use the testimony he gave the grand jury shortly after police found the bullet-riddled and charred bodies of Nicolle A. Lugdon, 24, of Eddington, Daniel T. Borders, 26, of Hermon and Lucas A. Tuscano, 28, of Bradford inside a rental car that was discovered on fire in the early morning hours of Aug. 13, 2012.

Defense attorneys for both Sexton and Daluz argued that Lanpher was entitled to claim his right under the Fifth Amendment, which protects a witness from self-incrimination.

“I’m going to rule that he has the Fifth Amendment right not to testify,” Justice William Anderson said.

Three other witnesses who testified Monday had connections to Mark Rowe, 26, of Brewer, who testified last week that he was with Sexton and Daluz the afternoon and evening of Aug. 12, 2012, and that he purchased Percocet pills from Sexton to sell.

Rowe’s ex-girlfriend Sarah Dougherty, 22, of Bangor testified that she hung out with Rowe, Sexton and Daluz in August 2012, and Rowe arrived at her house late on Aug. 12 and was “distraught” when he could not contact them. She also said that there was a gun in her home for “just a few days.”

Rowe, who lived in a garage apartment in Dedham in summer 2012, said he rented a motel room for Sexton and Daluz on Aug. 12, 2012, and the trio went to Carolina’s Bar & Grill.

Peter Cannon, a former employee of Carolina’s, took the stand Monday and said he saw Sexton and Daluz enter the bar. He said he cooked them a pizza and saw Sexton leave at about 10-10:30 p.m.

Rowe’s Dedham roommate, Darren Bishop, 27, testified that he saw a vehicle slowly drive past his rural house late on Aug. 12, 2012, and he later discovered a blue diesel can missing from his garage.

An investigator with the state fire marshal’s office and forensic scientist with the Maine State Police Criminal Laboratory in Augusta testified last week about finding a burned blue fuel can, which contained the remnants of diesel fuel, in the burned rental car.

Shortly after the morning break, Katelyn Lugdon, the sister of Nicolle Lugdon and the girlfriend of Borders, was brought before the judge for violating the conditions of her release on Friday, when she tested positive for drugs.

Anderson warned Katelyn Lugdon, who was arrested April 29 in Saugus, Massachusetts, after she failed to appear on April 28 for an interview with prosecutors, that if she was caught breaking the law, she could end up in jail until the trial is over.

Lugdon took the stand last week but is subject to recall. She testified that she and the victims had used and sold drugs.

Afternoon testimony came from Alyssa Abbott of Sullivan, who told the jury she, her boyfriend and Lanpher went to Bangor to buy heroin. She said the three of them met up with Sexton and Daluz at Carolina’s on the evening of Aug. 12, 2012. She said Lanpher and Sexton left for awhile, and when her group left to return home, Lanpher gave her cocaine.

The manager of the Ramada Inn took the stand to say Rowe rented a room by using cash on Aug. 12, 2012. A video played in court shows a man, who looks like Sexton, re-renting the room. The room’s electronic key was used at about 3:05 a.m. Aug. 13, 2012, and he said the system’s clock is about 12 minutes fast.

The burning rental car was discovered at about 3:30 a.m. by a woman on her way to work.

Two women also testified about seeing the rental car, with broken windows, at around 12:45 a.m. near the Ramada and at about 1:10 a.m. near the Wilson Street Walmart on Aug. 13, 2012.

Witness testimony will begin Tuesday at 9 a.m., the judge said when he dismissed the jury.