Downfall of officer in 'perfect murder'

But detectives harboured doubts about her death in January last year and arrested Mr Weddell for her murder. Subsequently released on bail, on Saturday Mr Weddell shot his mother-in-law dead before turning the gun on himself.

His world had been shattered in December when he learned she had been having an affair and wanted a divorce. Fearing that he would lose his three young children and his £450,000 family home in Dunstable, he drew on his experience of 25 years in the force to plot her murder.

Mrs Weddell, a nurse and part-time exam invigilator, was last seen alive on 30 January last year.

On the day of her death she had gone to work as usual at Queensberry School in Dunstable.

Colleagues said she was acting "perfectly normally". She returned to her home, where she would have seen her husband before he left for his 3pm shift.

But later the couple's three children were not collected from school as normal by their mother and friends and neighbours arranged to look after them until Mr Weddell could return from work.

When he got home he asked a neighbour to come with him to check the house for his wife. Significantly, it was noticed that he did not look in the garage.

Mr Weddell, 47, checked the house but the following morning again went to a neighbour's and said he had discovered his wife's body in the garage.

Mrs Weddell, who also worked at the Luton and Dunstable Hospital, was found with a cable tie around her neck and a suicide note nearby. Her husband later told detectives that the couple had rowed that morning and he had left for work earlier than usual.

At first it appeared he had got away with it. Mr Weddell was told that the death was "probably suicide", police released her body for a funeral and she was cremated.

But experienced detectives harboured suspicions about the killing.

Mrs Weddell's body showed no signs of a struggle and the injury from the cable tie did not look as though it could have been self-inflicted.

Forensic examination of the suicide note found that it had been typed out on the family computer. A linguistic expert examined the language in the suicide note and concluded it was more likely to have been written by Mr Weddell. Strangely no fingerprints were found on the note but there were marks consistent with having been made by a rubber glove.

Experts found the hard drive of the family computer had been turned on at 10.14am on 30 January, the day of the murder and turned off at 10.29am.

A court later heard that Mr Weddell was the only person in the family home at the time. Police were also concerned about the use of cable ties in the "suicide". Checks with police forces across Britain revealed only three previous deaths involving cable ties - and every one was a murder. Five months after the murder, police knocked at his door and arrested him for murder. Mr Weddell learned a week ago that his wife's mother, Danish-born Mrs Traute Maxfield, of Gustard Wood, Hertfordshire, had insisted she would be key witness in her son-in-law's murder trial - leading to speculation that it led directly to her death on Saturday.

On his arrest for his wife's murder last year he was suspended from duty at the Metropolitan Police and had his gun licence revoked.

On Saturday, Weddell apparently used an illegal shotgun to kill 70-year-old Mrs Maxfield before driving to the Broomhills Shooting Club in Markyate where he walked up a lane and shot himself dead. Today police are trying to establish how Weddell obtained the weapon.

Colleagues in the police force say they knew him as a diligent officer who enjoyed helping colleagues.

He worked as a police inspector in Barnet but was also the Police Federation representative for the local Operational Command Unit.

One said: "When we discovered he had been arrested for murdering his wife it took everyone by surprise. After he would not speak to anyone.

"But he always seemed a good bloke, you just don't know what goes on in some people's private lives."