When Randolph Alan Gaul was arrested last June in the slaying of 13-year-old Kathy Murphy of West Hyattsville, he gave a signed statement to detectives describing his tortured emotions in a chance meeting with the young victim.

"I didn't want to hurt anybody, but an indescribable resentment was building toward [a woman who had recently left him]," he wrote. "And when I say indescribable, I'm talking about a blind raging forest fire of a rage, and a resentment which masked that rage as a wool blanket might cover a window. The rage was hidden and totally unrecognizable. The resentment was its mask. . . .

"Emotionally I was regressing ever towards more primitive forms of my mature self. Horrors were building. My universe was on fire. I was becoming dangerous. I didn't know how to get out. I was lost-lost-lost. There was no 'me' left in the world."

With Beethoven, Mozart and a play by Jean-Paul Sartre, he concluded: "All I can say for certain is that Kathy Murphy is and was the one which elicited the emotional response. . . . There was never any doubt. And the agony of living with this fact has haunted me for two years now. Her ghost inhabits my soul. She lives on. I don't know how it could possibly be otherwise. My fate is sealed."

After signing the 12-page statement and answering detectives' questions, Gaul, now 32, was charged with the highly publicized slaying -- apparently the answer to an unsolved case that had baffled police since 1978.

Now, one week before the start of Gaul's trial, the seemingly airtight confession may be giving way to some serious doubts.

James E. Kenkel, Gaul's lawyer, maintains that his client is suffering from mental problems and has confessed to a crime he did not commit. Kenkel is trying to show that details in Gaul's statement had appeared in press accounts of the crime, and that some facts provided by Gaul contradicted what police know about the slaying. Without Gaul's confession, his attorney maintains, there is no other evidence to charge him.

Last week a number of local newspaper reporters -- including a reporter for The Washington Post -- were subpoenaed by county prosecutors as government witnesses at Gaul's trial, and instructed to bring along copies of all news articles written about the case.

Prosecutors apparently hope to refute any potential defense claim that all elements in the confession -- and in other statements Gaul gave police -- could have been obtained from news accounts. Although an official of the county prosecutors would not comment directly on the subpoenas, he expressed confidence in the state's case against Gaul.

"I would guess that there is a strong possibility something is there. This office doesn't have a reputation for wasting its time when there is no evidence," he said.

But at least one detail that police apparently believed had not been revealed at the time of the slaying did in fact appear in The Post and The Washington Star shortly after the slaying. That was the fact that Murphy's body had been left with a rock on her head. Gaul's knowledge of that detail was a factor in the authorities' decision to charge him, according to a source close to the case.

Gaul's lawyer is expected to claim that Gaul could merely have read the detail in newspaper accounts.

The case of Kathy Murphy began on the night of Aug. 23, 1978, when her mother asked her to come home instead of staying at a friend's house as planned. There is no telling what happened as Kathy Murphy crossed by Sligo Creek, a popular hangout for neighborhood youths who liked to smoke marijuana under the trees. What is known is that she never made it home. The next morning, her nude body was found lying face down in the creek's shallow water.

Police combed the area for suspects for weeks without success, despite tantalizing leads. Two neighborhood youths told detectives they had seen Murphy shortly after midnight near a bridge over the creek. The bridge was a shortcut between her home, located on Dayton Road, and the friend's house. Authorities also were told by one neighborhood teen-ager that he chased a shirtless, blond-haired youth through the park after he saw the youth following a teen-age girl.

(Gaul's appearance at a bond hearing last June was that of a young-looking, thin, sandy-haired man.)

For two years, Murphy's family lived without any hint of the identity of their daughter's assailant. One family member described it as living a "nightmare." A person close to the case has been told by police that at least two individuals earlier claimed they committed the crime. Neither was charged by skeptical police, who are used to having "confessors" take credit for crimes they did not commit.

Then one week last June, Murphy's family received a letter from Randy Gaul. They notified police. The next day Gaul called police and indicated he was staying in a motel in Bedford, Va., in the foothills of the Blue Ridge Mountains. Gaul was picked up and brought to Prince George's County police headquarters for questioning.

Advised of his rights and provided with coffee and crackers, Gaul wrote out his elaborate statement and then answered a detective's questions. A copy of the statement and a transcript of the police interview have been obtained by The Post.

"The power lines along with the Sligo Creek area was an area which was very familiar to me," Gaul wrote. "This was where I went to attempt to gain stock of my circumstances and my life for a period of approximately a week."

Gaul, a Navy veteran who had attended Northern Michigan University and the University of Colorado, said he had come to Maryland to be with his girlfriend. When he learned she was romantically involved with another man, he was devastated. "It must be remembered that I had fallen to an extreme level of emotional dependency -- in fact, distinctly childlike," he wrote. "This was the week which brought me to Kathy Murphy."

In happier days, he said, "sections of symphonies -- particularly Beethoven's Ninth and a turbulent Mozart symphony," went through his mind. But now, in his depressed state, "'No Exit' by Jean-Paul Sartre was the reading of the day."

After concluding with the declaration, "My fate is sealed," he signed the confession.

Police then began their interview.

"Did you force her to walk with you to the creek?" a detective asked.

"No," Gaul replied.

"What did you and Kathy do when you got to the creek?"

"We disrobed. . . ."

"What did you do with her clothes?"

"Folded them neatly. . . ."

"Was she sitting or laying down in the water?"

"She was kneeling in the water. . . ."

"Did you kill Kathy Murphy?"

"Yes."

"Are you telling me the truth?"

"As best as I remember it."

Kenkel, the county public defender and a former deputy prosecutor, has had an investigator working constantly on the case for months. A psychiatrist who has examined Gaul would not comment on Gaul's case specifically, but said in an interview that confessing to a murder that one did not commit is a desperate, publicity-seeking stunt, almost a form of attempted suicide.

Kenkel's investigator is carefully scrutinizing Gaul's confession for every possible detail that might contradict the known facts or reveal information that tracks closely to newspaper accounts of the crime.

Crime scene photographs, according to a source who has seen them, show that Kathy Murphy's clothes were not piled neatly by the creek, as Gaul's confession maintained. Some of the clothes were in the creek, others were strewn about.

Gaul's murder trial is scheduled to begin next week in a Prince George's County courtroom in Upper Marlboro before Circuit Court Judge Jacob S. Levin.