As avid Agatha Christie fans and founder members of the Florida Grim Death Club, Trepal and his wife Diana were in regular demand organising murder mystery weekends in which participants were given a script and acted out a grisly plot.
The victims always met a sticky end — there were drownings, beatings, shootings and strangulations. But at least half died from poisonings ... George Trepal's favourite form of murder.
As Ernest Prince, a fellow-member of the Grim Death Club, based in Bartow, Florida, was to recall: "If someone was going to be poisoned, George would find out exactly what symptoms they would get and how the crime could be investigated. He was always a real perfectionist when it came to poison. He seemed fascinated by it."
George Trepal was pretty smart. He was a member of the high-intelligence club Mensa. Diana Trepal was an orthopaedic surgeon and their inner circle of friends included nuclear scientists, college professors, writers and academics.
"Conversation at their dinner parties was pretty cerebral," remembered Nigel Walsh, who lived across the road from the Trepals' expensive split-level home. "We all knew about George's preoccupation with murder. It was just regarded as a quaint intellectual exercise. I thought him a real fun guy."
But the family who lived next door, Paul and Peggy Carr and their sons Duane and Travis, knew little about the pleasant side of George Trepal's nature.
For the six years they had been neighbours he had complained constantly about their noisy music, late-night parties and trespassing on his land. There was a long-running dispute over the sitting of a fence and damage that Trepal claimed had been done to his garden by the Carrs' three dogs.
But by October 1988, the Carr family had more to worry about than a neighbours' dispute. Peggy Carr, 45 and previously in good health, began suffering from nausea and aching joints. So did her two sons and a week later all three were in hospital.
The boys recovered slowly from the mystery illness but their mother got worse. After two months she slipped into a coma from which she never recovered. In March 1989 her family took the tragic decision to switch off the life support system and three days later, Peggy was dead.
FBI forensic investigators examined a number of Coke bottles thrown into a garbage container and discovered they had been laced with thallium nitrate, a rare colourless odourless poison banned in America since 1965. One gramme was enough to kill.
Who had been tampering with Coke bottles? An FBI investigation at the bottling plants revealed nothing and the neighbours, including the Trepals, were interviewed in order to eliminate them from the inquiry.
But seasoned detectives felt there was something strange about George Trepal. He seemed excited by the prospect of being interrogated and boasted how much he knew about crime, particularly murder. He told Detective Kevin Barrass: "I have made a study of violent crime and know that if I ever committed murder it would be the perfect one."
Barrass would later tell a court: "He seemed determined to leave us in no doubt that we were in the presence of a superior intellect. I was left feeling that he was desperate to tell us something but knew it would be unwise to do so.
"I later told my superior that I thought we should further investigate Trepal but if possible without his knowing." As a result undercover detective Susan Goreck, 35, was put on the case and instructed to get to know the Trepals and if possible become friendly with them.
Goreck arrived in Bartow posing as a freelance computer-programmer working from home and rented a house near the Trepals. Eventually she was invited to one of George Trepal's murder weekends and was soon a regular attender.
She said later: "I found George Trepal a charming man, interesting to be with and very amusing. It did not take me long to discover that he had an obsession with murder, particularly involving poison, and had a large library on the subject.
"When I asked him why, he said that he had originally taken a degree in chemistry before transferring to computer science. He also said that he was certain that a skilful poisoner could really outwit forensic scientists.
"When I once asked him whether he thought he could commit the perfect poisoning, he just smiled and said: 'That would be telling.'"
Soon Susan Goreck was a regular guest at the Trepal house and was frequently invited to meals there. She remembered: "Although I had no proof I was beginning to suspect that George Trepal had more than an academic interest in poisons.
"I was now becoming increasingly cautious. If we were eating together and I had to go to the bathroom, I wouldn't eat anything I'd left at the table. I had to be very aware at all times."
In December 1989, the Trepals moved to Seabring, Florida, so that Diana could open a new orthopaedic practice. They were looking round for a tenant for their Bartow home and were delighted when Susan Goreck offered to move in. They would have been less delighted had they known that they day after they moved to Seabring, FBI forensic experts were examining the house from cellar to loft.
It was a worthwhile operation: not only was a phial containing thallium nitrate found in a cupboard but also a copy of Agatha Christie's whodunnit The Pale Horse - a tale about a pharmacist who kills by putting thallium nitrate into food and medicine. The relevant paragraphs were all marked in pencil.
George Trepal, vehemently protesting his innocence, was arrested three days later and charged with first degree murder. His friends were shocked and astounded. Ernest Prince said he spoke for them all when he told the media: "I found it impossible to believe that George could do anything like that. I have known him for years. He is a great guy, always helpful and friendly."
But the jury heard another side of the genial computer boffin when Trepal appeared in court in Miami in August 1990. He tried to lay the blame for the Carr family killings on his wife Diana, claiming she had obtained thallium nitrate from a hospital at which she was consultant.
District Attorney John Aguero was quick to acquaint the jury with the prosecution's view: "This is the most diabolical man you will ever see before you in your life. What we have here is a man who thought he was so smart that he could commit the perfect crime. But he was not so smart."
It took the jury six hours to find George Trepal guilty. Then they heard the truth about the man they had convicted: for over 20 years Trepal had been drug-crazy. As a student he tried to poison room-mates.
And in 1975 had been jailed for two years for being involved in manufacturing methampetamine - commonly known as crack. One of the ingredients of this drug is thallium nitrate.
Members of the Carr family were in court as Trepal was sentenced to die in the electric chair.
Afterwards, Peggy's sister Mary declared: "I would personally like to turn on the electric current and kill this monster. I have lost my sister and I believe in an eye for an eye and a tooth for a tooth."
Fifteen years later, Trepal is still in Florida's Death Row, hoping to escape the electric chair by a series of appeals. Before she returned to the shadows, the woman who brought him to justice, undercover agent Susan Goreck delivered her verdict on George Trepal. "I think he killed for sheer intellectual pleasure," she said. "It was a game to him. What really upset him was not being able to commit the perfect crime."