There was much sympathy for Peter Heron when he found his wife, Ann, murdered in their home on the outskirts of Darlington.

But all that evaporated after a few days, when it was revealed that he had been seeing a barmaid. In the second part of our exclusive series, Mr Heron's daughter, Debbie Simpson, tells Chris Lloyd for the first time of the affair that changed everything

'THE affair was a very big shock. It changed everything in terms of the investigation," says Debbie Simpson.

Shortly after Mrs Simpson's father found her stepmother murdered in their secluded home on the outskirts of Darlington, a second "bombshell" exploded. A national newspaper revealed that Peter Heron - Debbie's father and murdered Ann's second husband - had been having an affair with a barmaid.

"It changed the direction of the investigation and I think the police became tunnel-visioned about it being the motive," says Mrs Simpson.

"It changed the tone of the reporting and of people's sympathy. They thought: 'He's been having an affair - case solved'. Quite often, it is the family, it is a domestic. But in this case, it isn't.

"The facts speak for themselves and still, after 18 long years, the case remains unsolved." In fact, it is the only murder in County Durham for 55 years where the identity of the killer remains undetected - although, partly because of the affair, many people believe they have solved the case in their own minds.

"In a poll, 90 per cent of people would say that Dad's guilty. I want to challenge that perception. I ask the public to read these articles objectively and dispassionately, as I have tried to put them together, and decide for themselves whether or not this case is cut and dried or whether it warrants further investigation.

"Just because someone is having an affair, it doesn't make them a murderer."

In a bid to clear her father's name and find the real killer of her stepmother, Mrs Simpson, 46, is speaking publicly for the first time to The Northern Echo about the events of that terrible day, Friday, August 3, 1990 when Mrs Heron, 44, was murdered.

Mrs Heron spent the afternoon of the hottest day of the year sunbathing in the grounds of Aeolian House, isolated off the road between Darlington and Middleton St George.

Mr Heron, her husband of four years, had returned from work at about 5.50pm to find her body in the lounge. She had been savagely stabbed in the neck and her bikini bottoms had been removed, although there was no evidence of a sexual attack.

Nothing in the house had been touched. There were no signs of a struggle.

The radio played on.

A book appeared misplaced - it should have been beside the sunlounger where Mrs Heron had been reading it, but instead was about 15 yards away with a pair of shoes beneath a tree.

Heidi, the collie dog on which Mrs Heron doted, was terribly distressed. It would never again trust a strange man.

The first line of inquiry reported in The Northern Echo was that Mrs Heron, a regular sunbather, had been disturbed the week before by a prowler who had walked up Aeolian's driveway. His presence had forced her to go inside.

On the day of the murder, a farmer had been harvesting in a field next door to Aeolian, kicking up a cloud of dust. To get away from it, Ann had moved her sunbed to the front of the house, which meant she could be seen, lying in her bikini, from tall vehicles - lorries, buses - passing on the A68.

Two days after the murder, police said they were trying to trace a dark blue Ford Sierra which had been loitering outside the house that afternoon. Witnesses - a taxi driver and a family of four returning from the beach - also reported seeing a blue car rush down Aeolian's drive and speed dangerously through the traffic at about 5pm, the time the murder was probably committed.

"The sighting of the blue car gave us hope," says Mrs Simpson. "Who and why were the main questions we kept asking ourselves. It is still the question that matters most: the car was seen leaving at high speed and featured in all the media and television reporting at the time, including an episode of the BBC Crimewatch programme.

"The driver, described as being dark haired, suntanned and in his early 30s, has never been traced."

Four days after the murder, Mr Heron, then aged 53, took part in a highly-charged press conference at Darlington police station, asking for the public's assistance. Through tears that shook his whole body, he said: "I appeal not for my sake, but for Ann's sake. She was a beautiful lass. She would not know how to hurt anybody. Her eyes sparkled. Nobody could fail to love Ann. It was the best time of my life when I met her ten years ago."

After the conference, Mr Heron left Mrs Simpson's care at the Blacksmith's Arms pub, in Swainby, North Yorkshire, where he had been staying since the killing, and returned home.

"I didn't want him to go back to Aeolian," she remembers. "I didn't want him living there on his own.

"There was the lounge with no carpet because it was heavily blood stained and the police had taken it away for examination. A friend had gone to the house to try and sort the floorboards for him.

"I would say, 'you can't go back, what if he comes back?'. Dad was so down he said something like, 'it might be better if he did'.

"We would press him to come through to us for meals because to this day he can't cook. He would have been living on a cup of tea and a piece of toast and we would feed him on scampi and chips."

Six days after the murder, there was a knock on the door at the pub. Mrs Simpson remembers: "There were two men there, one a photographer and the other a reporter who said: 'I want to ask Mr Heron about the affair.'

"I pulled myself up to my full 5ft and said: 'I beg your pardon, what affair, you'd better get your facts right before putting anything into print.'

"Then I picked the phone up and rang Dad. He said straight away, 'Yes, I'm sorry, Deb, it's true'."

For ten months, Mr Heron had been seeing a part-time 32-year-old barmaid at his golf club at Dinsdale Spa. The woman had told police that the affair was over and she was trying to patch up her marriage.

"It was a very big shock," says Mrs Simpson. "We had no inclination whatsoever. I was disappointed in him, if I'm honest.

"But when the story broke, he certainly didn't hide it. There was a lot of speculation about whether Ann would have known, but he is adamant that she didn't."

The revelation, though, changed the way the case was perceived. Mr Heron was no longer cast in such a sympathetic light.

"In the early days of the investigation, he was asked to join an identity parade for a guy who had reported seeing a white car which he thought was about to turn into the driveway of Aeolian," says Mrs Simpson.

"Dad went down to the police station as requested in his black tie - he wore black for quite while after.

"By this time he had appeared on television and also in the media. The policeman said to the witness, 'Is the suspect in the line-up?'

"The guy walked up and down and said it's number ten. Dad was number one in the line. The police officer said at least twice 'are you sure?'.

"But that terminology, 'the suspect' really shook him. It was probably his first indication of the way the investigation was going."

And it wasn't just the police. "Six months after it happened," says Mrs Simpson, "Dad was in the garden at Aeolian and some kids walked past at the bottom of the road and they shouted 'murderer' and that really, really upset him."

For Mrs Simpson, and her twin sisters, Jacqui and Beverley, it was awful to see their father suffer. Not only had he to cope with the trauma of finding his wife murdered and then the embarrassment of his private life being laid bare before the public, he also had to contend with the finger of suspicion being pointed at him while he was trying to grieve.

"That first Christmas morning," says Debbie, "at about eight o'clock the phone rang. It was Dad. He was in the car. I said 'where are you?' and he said 'I'm just driving into the cemetery'. He'd got up early and driven all the way to Scotland where Ann's ashes are buried.

"It was heart-wrenching."

In the summer of 1992, a little happiness filtered into his life.

Freda Buddie was a 49-year-old widow who was a receptionist for one of the client's of Peter's haulage business, GE Stiller (Transport) Ltd, of Middleton St George.

She lived in Motherwell where she was well-known as a church and charity singer.

"She was the sort of person who would light up a room," says Mrs Simpson.

Through business visits, they struck up a relationship. "It was about a year-and-a-half afterwards. It did seem quite soon and that probably has also worked against him."

In fact, they walked out of the church in Motherwell in January 1993, having just got married, to be greeted by a flash of press photographers who were intrigued by the situation.

Even on his wedding day, Peter Heron was unable to escape the ghost of suspicion. And after settling in Motherwell for a decade where, in 2005, he nursed Freda through terminal cancer, it still haunted him.

On the morning of her funeral, the police phoned. Four months later, they knocked on the door to arrest him on suspicion of murder