A surprise prosecution witness Thursday wrapped up the state’s case against Nathan Wade Conley of Norway, one of three teen-agers on trial for the shooting death of hay farmer Lucien Frechette.

In another courtroom, the defense cases of Jay Snow and Christopher Fitch closed Thursday afternoon and juries for the Norway teen-agers were instructed to return to court Monday to begin deliberations in Frechette case.

The victim’s grandson, Roger Coffin, testified in both courtrooms, placing all three boys near the crime scene within two weeks of the April 1988 slaying of his grandfather.

Coffin’s testimony was entered in the case against Conley, but Justice Stephen Perkins denied the request to admit Coffin’s testimony as evidence before jurors in the cases against Snow and Fitch. The prosecution had rested in those cases on Tuesday. Assistant Attorney General Tom Goodwin said the testimony was denied because it “just came too late” and was apparently considered of limited value.

Coffin had been subpoenaed to testify in the simultaneous, yet separate, trials of Snow, Fitch and Conley, all 17, on murder and robbery charges in Frechette’s death. But what he told Conley’s jury just before noon Thursday only came into the hands of authorities on Wednesday.

A fourth suspect, Shari Brown, also 17, testified against the boys earlier this week in exchange for being allowed to plead guilty to similar charges in juvenile court.

Coffin, who said he had no question that the defendants were the boys he saw on or near Crockett Ridge Road on two occasions, testified that he didn’t make the connection immediately after Frechette was shot.

When police questioned him the day the body was found, he told the jury, “I didn’t think that young children were suspects, so I didn’t think anything of the boys I’d seen a week or two before.”

Police also had been investigating the possibility that one of Frechette’s hay customers may have killed him.

Coffin testified that he saw Fitch and Conley on one occasion, and a few days later saw them with Snow. He said that he remembered the sightings just last summer, when he recognized Snow’s picture on television after Snow was arrested.

Under questioning by James Andrews, one of Conley’s two attorneys, Coffin testified that he went out for a walk with his wife after supper the day of the shooting, around 5:40 p.m. He said he saw some vehicles drive by, then heard gunshots as they walked back home.

“I thought it was my neighbor, target-practicing,” he said.

One of the issues the defense has pressed is whether Conley, who in testimony frequently has been referred to as Wade, and the others were likely to be in the area when neighbors heard the shots. Brown testified that she drove the boys to Crockett Ridge Road in her mother’s car before returning to pick up her mother at work.

The defense brought in Brown’s mother, Brenda Buck, later in the day to testify that she got out of work around 5 p.m.

Coffin’s unexpected testimony came in a roundabout way. He mentioned the incidents to his uncle last week, he said. The uncle told his daughter, who called authorities this week. A police officer approached Coffin about it on Wednesday.

In the courtroom where Snow and Fitch were being tried — in the testimony which was rejected — Coffin said he knows now that the three boys he saw were Fitch, Snow and Conley.

“You want these boys to get convicted, don’t you?” charged Alan Stone, who is defending Fitch.

“It isn’t up to me,” said Coffin, “it’s up to the jury.”

Also during Conley’s trial, Assistant Attorney General T. Gregory Motta put state police Detective Peter Herring on the witness stand to testify about his questioning of Conley in connection with the case. A 20-minute recording of that interview, most of it unintelligible, was played in court.

John Jenness, Conley’s other attorney, questioned an Oxford County Jail guard who had escorted Brown to one of the pretrial hearings in the case. David McAllister testified that he heard Brown tell two other girls that if another boy who was implicated but not charged in the case “didn’t stop laughing at Wade, she would spill the whole can of beans on him and Wade.”

Brown had testified on Wednesday that she didn’t recall making such a statement.

Also testifying as the defense opened its case for Conley were a private investigator, who identified for evidentiary purposes several photographs of the area around Frechette’s home, and two of Frechette’s neighbors, both of whom testified that they saw no one unusual in the area around the time of the shooting.

Conley is expected to testify in his own defense on Friday.

Among those testifying for the defense Thursday in the Snow and Fitch trial in the other courtroom was Gaynor Fitch of South Paris, father of Christopher Fitch, who said he once owned a pearl-handled .22-caliber pistol which disappeared more than 10 years ago.

Frechette was shot three times in the back of the head with .22-caliber bullets, according to an autopsy.

Cindy Rioux and Kelly Finn, both of Norway, also testified about a conversation they had with Brown in 1989 in which Brown stated she would lie to get someone in trouble. The defense was attempting to discredit Brown’s earlier testimony for the state at the murder trials.

Jeff Gilman and Melissa Vinton were called by the defense to testify about a conversation they had last year with Brown, who implicated another person as being responsible for the Frechette death.

Goodwin said attorneys in the Snow and Fitch trial will meet with Perkins on Friday to go over what instructions will be given to both juries. Snow’s panel will report to the courthouse at 9 a.m. and Fitch’s at 11 a.m.

Final arguments will be given by the state and both defense attorneys before the judge instructs jurors on the laws.