Barry George became a suspect for the murder of Jill Dando because he was, in the words of his defence counsel, “the local nutter”. He was a loner, an obsessive and a fantasist who created a world in which he was related to Freddie Mercury and had served in the SAS.

At the end of 1999, eight months into the investigation into the fatal shooting of Miss Dando on the doorstep of her Fulham home, there was no suspect and police had embarked on a wholesale review of the evidence in the case.

Mr George had cropped up, sometimes as Barry Bulsara, but he had not come to the fore. He appeared to be the man whose behaviour had concerned staff at a disability advice centre and a minicab company in the days after Miss Dando was shot. This man appeared to be trying to concoct an alibi and persuade people to vouch for his whereabouts on the day of the murder.

Detectives decided that Mr George warranted further examination, and the more they looked at him the more intriguing he became. A search of his squalid flat found piles of newspapers and celebrity magazines, including copies of the BBC in-house publication Ariel relating to Miss Dando. He had had an obsession with Diana, Princess of Wales, and had pinned a poster to the gates of Buckingham Palace after her death with the words “Queen of Hearts” and signed “Barry Bulsara”. Bulsara was the name of a relative of Freddie Mercury.

Mr George then transferred his obsession to other celebrities. There were pictures of Anthea Turner and Caron Keating among his magazine collection. Of greater concern to detectives, however, were the dozens of rolls of film containing 2,248 pictures of 419 different women. The photographs had been taken by Mr George as he stalked women around Hammersmith and Fulham — often accosting them, asking for dates or following them to their homes.

He was placed under surveillance and was seen to approach 38 women during a three-week period. He also visited internet cafés and looked up information on DNA tests, surveillance techniques and new identity services.

Checks revealed convictions for indecent assault in 1982 and attempted rape in 1983 and more than a dozen women had complained to police about him. Another photograph showed Mr George in military clothing carrying a handgun and further investigations uncovered a longstanding interest in guns.

It was not until forensic scientists discovered a microscopic speck of gunpowder in the pocket of a coat found in Mr George’s home that detectives felt they had a strong enough case. Hamish Campbell, the Scotland Yard detective in charge of the most difficult inquiry of his career, believed there was now enough evidence to charge Mr George with murder.

The first Old Bailey trial saw intense concentration on the importance of that tiny particle of firearms discharge residue and culminated, in July 2001, with a jury returning a majority guilty verdict after five days of deliberation. It was a controversial conclusion and the foreman of the jury was later to reflect that had the evidence been presented differently there might have been an acquittal.

Yesterday, a juror from the original murder trial said she was always “deeply concerned” about the conviction.

Janet Herbert told ITV News she repeatedly phoned the court after the case to express her concerns, but was left with nowhere to turn.

She added: “I’ve always felt deeply concerned about the verdict that was reached, and deeply concerned that somebody had been put in prison for life that possibly hadn’t committed this crime. I have to say there’s never been a time I’ve not thought about it. It’s always worried me greatly.”

A campaign followed that saw Mr George presented as a mentally inadequate man who could not have been capable of carrying out the murder.

The Court of Appeal disagreed at his first appeal hearing in 2002 and he remained in prison. A second appeal hearing was won in 2007 on the ground of a major reassessment of the gunshot residue evidence. Scientists were now sceptical of the significance of the particle, which measured 1/2000th of an inch. Three senior judges ruled that the speck which had convinced police that Mr George could be charged in the first place could now support his appeal case.

There was, however, other evidence that warranted a retrial of Mr George. The trial judge rejected attempts by the prosecution to put the gunshot particle before the new jury. Following changes in the law, which allowed the Crown to present evidence of “bad character”, a jury could hear for the first time of Mr George’s harassment and stalking of women in the area where he and Miss Dando lived.

Jonathan Laidlaw, QC, for the prosecution, was allowed to tell jurors of Mr George’s “many years” during which he “spent a great deal of time watching and following single women”.

Mr George’s previous convictions were not disclosed but the court heard from 14 women who said that he had followed or frightened them.

The prosecution case attempted to build a circumstantial case that pointed to Mr George’s guilt. There was no tangible evidence, however — no science and no witness — to place him at the murder scene. William Clegg, QC, for the defence, closed by putting the misfit-not-murderer theory more bluntly. Was Mr George capable of executing Miss Dando in cold blood, escaping the scene and eluding a huge police manhunt for a year?

Mr Clegg asked: “Who was the man who outwitted Campbell of the Yard? Our Barry — what do you think? Light bulb’s flickering maybe but remember, it is only a 40-watt bulb when it is completely lit.”

After two days’ deliberation the jury of eight women and four men agreed with that assessment and set him free.

So who did kill her?

— Police considered the possibility that a criminal gang had sought revenge after being featured on Crimewatch, which Jill Dando co-presented

— Detectives looked at the possibility that a contract killer had been hired to shoot her in revenge for someone’s conviction. But they eventually ruled that out

— At the first trial Mr George’s barrister, Michael Mansfield, QC, revealed a plot that included Radovan Karadzic. A National Criminal Intelligence Service report suggested that a hitman was following the orders of Arkan, the Serbian warlord and Karadzic enforcer, who wanted retaliation for the Nato bombing of a television station in Belgrade. Miss Dando was thought to have angered Serbs after she presented a programme raising money to help Kosovan orphans in 1998

— Other theories focused on whether a jealous ex-lover had harboured murderous intent after she announced her engagement to Alan Farthing a few months earlier. Police ruled out that suggestion

— Her brother, Nigel, had told detectives that she had been concerned about “some guy pestering her”. There was a supposed fan called Julian who had approached her days before her murder and fitted the description of the suspect seen near the home. He may have been the man seen loitering near Miss Dando’s house wearing a trilby and baggy suit on the day she died

Times Recommends

• Donor organ allowed child’s own heart to heal
• Michael Jackson: Not the final chapter
• Brüno toned down for 15 rating