Cranog Jones, 44, from Cheltenham, Gloucestershire, had denied trying to poison his wife Margaret, 42, with a 2ft square box connected by a pipe to the exhaust of her car, in December 1991.
Mrs Jones had told Winchester Crown Court of waking up to find her husband crouching beside her bed poised to place a device 'rather like a diver's helmet' over her head.
Christopher Clark QC, for the prosecution, said the pipe was connected through a hole that Jones had drilled in the bedroom wall of their cottage at Brockhampton, to the exhaust of her Ford Fiesta which was in the garage. The engine was on full choke so that carbon monoxide was going into the piping.
Jones, head of training and education at Smiths Industries, who was then divorcing his wife, had planned to move her body to her car to make the death look like suicide. He had already gassed the family cat with the contraption during a trial run.
Mrs Jones was awakened by the sound of the gas which her husband had failed to muffle with a duvet. Mr Clark told the court that she quickly 'put two and two together', and asked her husband if he was trying to kill their daughter, Cassandra, as well.
She ran to a nearby telephone box to call the police because the phone at their home had been pulled from its socket. She then hid behind the wall of a local chapel 'cold, shaking and shivering' until she saw her husband drive past in his car.
Jones, who has since remarried, had claimed he was 'set up' by his wife and that she was out to destroy him. He said he had drilled a hole in the bedroom wall to build a vanity unit sink in the bedroom. It was to be a birthday surprise for her. He claimed he had disposed of piping he usually kept in his garage because it had dawned on him that his wife was planning to set him up.
The court was told that the couple, who were married for 20 years and had three children, had marital difficulties. Mrs Jones said it was an unhappy union because of her husband's affairs. He had left the family home, but returned six weeks before the murder attempt.
The jury found Jones guilty of attempted murder after six hours' deliberation. He will be sentenced today.
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