Kevin Lane, 47, was convicted in 1996 of the murder of car dealer Robert Magill, who died in an execution-style shooting in Chorleywood in 1994.
Lane, of Potton, has always claimed he is innocent and yesterday took his case to the Court of Appeal in London.
His lawyers say his conviction is ‘unsafe’ because a ‘spectacularly corrupt’ detective was involved in the case.
But after hearing a day of argument, Lady Justice Rafferty, Mr Justice William Davis and Judge Melbourne Inman QC opted to reserve judgment on the case.
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Lane was jailed at the Old Bailey in 1996 over the killing of Mr Magill, who was shot dead as he walked his dog.
He was shot five times in Valley Road, before the gunmen escaped the scene in a BMW. Lane was convicted after a retrial and served 20 years before his release on licence in January this year.
Yesterday, dressed in a smart blue suit, he was back inside a court, as his barrister Joel Bennathan QC outlined evidence which is said to make the conviction ‘unsafe’.
The QC said Det Sgt Chris Spackman was not only corrupt, but in 2003 had been jailed himself for a plot to steal £160,000 from Herts Police.
There was evidence he had set up a cannabis factory, having arranged for plants to be stolen from a field, using a police radio to ensure non-corrupt officers did not come across the theft, he added.
And when he was finally arrested, he was found to be wearing a designer watch, which had been an exhibit in a case he was involved in and which had gone missing.
But the detective’s misconduct was not only in relation to actual crimes, as there was also evidence that he had been ‘misbehaving’ at the time of Lane’s trial at the Old Bailey.
“There were things going on at the time which showed signs of Spackman’s misconduct,” said the barrister. “Mr Lane was saying at his trial that Spackman was lying.”
Court papers revealed evidence of a conversation between Spackman and lawyers in which he had either lied or revealed that he had access to papers he should not have been able to see, said the QC.
Lane’s co-accused at the trial had also said at the time that Spackman was ‘very determined and bent’, Mr Bennathan told the judges.
He said it therefore could not be suggested that complaints about the detective only arose after conviction.
Arguing that the murder conviction was therefore ‘unsafe’, he said courts need to be able to put ‘enormous faith and trust’ in the integrity of detectives investigating serious crimes. The judges did not set a date when the judgment will be given.