WHEN THEY FOUND HER IN THE stage-managed chaos of her ransacked home, 47-year-old Marilyn Reza was tucked under a warm blanket with a pillow placed carefully under her head. There wasn't even much blood from the bullet wound in her brain. Suffolk County homicide detective Bob Anderson stood at the foot of the bed in the comfortable Dutch Colonial house and came to a quick, professional conclusion. "Whoever killed her, it was someone who loved her," he thought to himself.

The first press reports, however, put a different spin on the story—an explanation that suited the suburban nightmares of residents in the affluent Long Island town of Bayport, N.Y. The newspapers reported that Marilyn Reza was the apparent victim of a burglary gone bad—although as time went on, things reported stolen kept reappearing. She had been home alone that night last December, writing Christmas cards, when a killer slipped into the five-bedroom house and shot her in the head, then wrapped a necktie around her throat to make sure she was dead.

There were no witnesses, no suspects. Marilyn's daughters, Elizabeth Joy, 20, and Kristyn, 18, were off at school. Her husband, Dr. Robert Reza, 47, a prominent pulmonary specialist, was attending a medical convention in Washington, D.C.

Meanwhile, Anderson, 45, and his partner, Anthony Laghezza, 53, veterans with 45 years of police service between them, made a cautious tour of the white shingle house on South Gillette Avenue. Neither detective could shake the sight of the victim so tenderly laid out on her bed. And they both heard a silent alarm of false clues: flagrantly open dresser drawers whose contents were disturbed, though not looted, and the front door, which was open but unbroken. The two detectives exchanged knowing looks and sealed the crime scene.

"We both knew this was no burglary," says Anderson.

By most accounts, the person who loved Marilyn Reza most was her husband. But he seemed beyond suspicion. For one thing, he had a seemingly airtight alibi—the convention in Washington. For another, almost everyone said that Bob and Marilyn Reza had an ideal marriage. After 22 years, they still held hands on long soulful walks through the south-shore towns of Long Island. They were devoted members of their church and sang in the choir.

Det. Sgt. Robert Doyle, 40, assembled a team of 10 homicide specialists and began the arduous leg-work of investigation. Marilyn Jeffries had grown up on a farm in Pennsylvania. She became a nurse and met Robert Reza—the oldest son of H.T. Reza, a minister in the Church of the Nazarene—when he was a student at Columbia University's College of Physicians and Surgeons. They were married in 1968 at the university chapel. In addition to maintaining the medical practice that brought him a six-figure annual income, Bob Reza was a pillar of his community, as well as a former elder at the New Life Community Church. But there were indications that the Reza marriage was troubled. "We found out that they had been under-going counseling for five years," says Doyle. In spite of his own domestic problems, Reza served as a family counselor for his church.

In time, police observed peculiarities in Reza's behavior. With his daughters by his side, he held a press conference lavishly praising the police for their devotion to solving the case. The police found it odd that nothing was missing from the house. But it was the doctor's exaggerated, bubbling eagerness to help, as if he were trying to pick their brains, that set off alarms among the detectives. "He called us 10 times a day asking if he could do anything," recalls Anderson.

It was only after detectives went back and talked to Reza's colleagues that the widower's model-citizen image began to crumble. "He was in reality a tyrant," says one investigator, noting that Marilyn ran his office. "He'd scream at Marilyn in front of other doctors, in front of patients. He was not a happy man."

Just eight days after the Dec. 12 murder, Anderson and Laghezza brought Reza to police headquarters at Yaphank, N.Y. There, authorities laid out their telling case. They told Reza they believed he had secretly flown back to New York City from Washington to kill his wife and had then returned to the conference to establish his alibi. In addition to his original airline shuttle tickets, they had a copy of another ticket in his name from Washington to New York for Dec. 11. They produced parking receipts from LaGuardia Airport showing that he had left his car in parking lot No. 4 when he departed for Washington on Dec. 10 and had retrieved it from parking lot No. 1 on the 12th, indicating that the car had been used between those times. But most damning was Reza's hotel bill. The conference was to last through Friday, Dec. 14. The hotel receipt clearly showed that Dr. Reza checked out at 10:15 A.M. on Wednesday, Dec. 12, perhaps, police believe, anticipating the discovery of his wife's body. It was also almost two hours before he was notified of his wife's death. At the array of evidence, Reza broke down and, police say, confessed. But first he insisted on calling his elder daughter, Elizabeth Joy. "I killed Mommy," he told her over the phone. Then he signed a meticulously detailed 12-page confession:

"Shortly after Thanksgiving 1990, I was so frustrated with my life, and I decided to buy a gun and kill my wife, Marilyn," he said in the confession. When he sneaked back to Long Island on Tuesday night, the 11th, Reza drove home from the airport, parked behind the house and found his wife writing Christmas cards by a fire. "We spoke briefly and went to bed about 11:30 P.M. She took half of a Halcion [sleeping pill].

"As soon as I was sure she was sound asleep ... I got up and went into Elizabeth Joy's study room and got my .22 caliber rifle. ... I approached Marilyn's side of the bed, held the rifle...three to four feet from her head.... I wanted to put the bullet through her brain to kill her quickly.... I pulled the trigger once and the gun went off.... I messed up the drawers to make it look like a burglary ...." Reza drove back to the airport, left his car in another lot, then used a car service to Manhattan where he took the early-morning Metroliner to Washington.

Dr. Reza pleaded not guilty to homicide charges and was held on $5 million bail at the Suffolk County prison in Riverhead, where he is still visited by his daughters and other members of his family. The confession, which will be challenged at hearings this summer by his attorney, Paul Gianelli, as having been extracted under emotional duress, threw the community into turmoil. The pastor of Reza's church, John W. Smith, told his parishioners that he was "used" by Reza and "would have defended him to the death." But alter reading the confession, Smith said, he became angry and was convinced that Reza was guilty.

Yet investigators were still not satisfied that they had the whole story. "It didn't make sense," says Doyle of Reza's stated motive—that his wife was "too perfect" and he couldn't cope with success. Then the church organist, Kathy Senese, 36, a mother of three, came forward with a more prosaic explanation. She and Dr. Reza had been having an affair since before her separation from her husband, Sal, 37. Reza had given Kathy marriage counseling. His murder confession opened her eyes.

Reunited last winter, the Seneses sat in the living room of their Sayville home after Reza was arrested, and tried to explain what happened. "We were childhood sweethearts," says Sal, a computer programmer. "We started to have problems about a year ago. Not communicating. Reza manipulated Kathy when she was vulnerable."

Leaning closer to her husband, the whisper-thin Kathy asks in a pleading voice, "Why didn't I see that? Why did I see only good things? Please don't say I'm dumb."

"She was vulnerable, and he was a big shot, and he took her to opera," says Sal. "A master manipulator. A phony."

"He told me I was worth something," says Kathy. Then she straightens in her chair. "But this will never happen again," she vows.

It was Kathy's final, crucial bit of testimony that gave authorities the completed picture they wanted. She told police that Reza had told her after Thanksgiving, "If anything should happen to Marilyn, don't feel guilty. I may look distraught, but I won't be."

At the New Life Community Church, no one speaks on the record anymore. Kathy Senese—who played Marilyn's three favorite hymns at a memorial service—has been fired as the church organist. Smith and his family were sent on vacation to avoid the publicity. If people are astounded by Reza's behavior, that is understandable, says Doyle. After all, he and his wife more than doubled the tithe given to the church by other worshipers. And Reza was by no means an unpleasant man. "He's likable," says Anderson ungrudgingly. "In fact he was the nicest murder suspect I ever went after."