Twenty years ago on Friday, 26 April, a gunman knocked on the door of Jill Dando's house in Fulham, west London, and shot her dead.
Barry George, a local man with an IQ of only 75 and "severe cognitive impairment", was convicted of murdering Ms Dando, 37, in 2001 but was acquitted at a retrial in 2008 after the reliability of gunshot residue evidence was undermined.
Retired Detective Chief Inspector Hamish Campbell said earlier this month he believed the killer would never be caught.
So who might have committed the crime and why?
Celebrity Stalker
The prosecution claimed at two Old Bailey trials that the killer was obsessed with Ms Dando, who regularly presented the BBC news and also fronted Crimewatch UK and several other popular TV programmes.
But if George was not the killer, is it possible Ms Dando had another stalker?
Detectives reportedly discovered 140 people who were in various degrees "obsessed" with the attractive blonde presenter.
She received thousands of letters, some of which were quite disturbing and included sexually explicit "fan mail."
"There were some odd letters she received and one individual who was clearly obsessed," DCI Campbell told a documentary, which was broadcast on Thursday, 25 April.
Police checked out all 140 of Dando's super-fans and were confident none were in Fulham on the day she was killed.
Her sister Judith said Dando tried to be "nice" to the obsessives, even when "they made her life difficult."
Serbian Hitman
One of the most extraordinary alternative scenarios around Dando's death involves Serbia.
Conspiracy theorists argue she was assassinated by Belgrade in retaliation after Nato forces bombed Serbia.
Three days before she was killed British planes bombed a Serbian TV station in Belgrade, killing 16 members of staff.
"My mother did tell me the Serbians had said when they bombed their broadcasting station that we'd killed the Jill Dando of Serbia. The fact it might have been a tit for tat reprisal, I can understand that might be the case, particularly since the way Jill was killed it makes me think it's related to something bigger than the actual act," Dando's sister Judith was reported as saying in the Mirror.
The conspiracy theorists point out Dando fronted a charity appeal for Kosovan refugees only a few weeks before her death, which may have infuriated Serbian nationalists.
Around the time of the murder a traffic warden noticed a blue Range Rover parked illegally but she only took down part of the licence number when the driver protested and drove off.
The Range Rover was seen by other eyewitnesses and there has been speculation it was linked to the killing.
But the Belgrade connection does not hold much water.
"I think you can rule out a Serbian hitman, that was a popular theory doing the rounds at the time," her brother Nigel Dando told TV presenter Lorraine Kelly earlier this month.
Killed by a Gangster
Another theory which has been put forward suggests she was taken out by a professional hitman paid by a big time gangster who was angered by her involvement with Crimewatch UK, a programme which helped the British police catch criminals.
Kenny Noye, a gangster who was jailed for life for a road rage murder on the M25, was reportedly infuriated because Dando interviewed a witness whose involvement led to his capture.
There has also been speculation that Liverpool gangster John Haase may have provided the gun used in the crime.
Nick Ross, who co-hosted Crimewatch with her for many years, rubbished the theory in a documentary aired earlier this month.
"Right from the beginning there was this assumption it was something to do with Crimewatch. To go for someone who is just the messenger? Why? Sure she was the Crimewatch presenter, but why not for presenting the holiday programme? Why not just because she is famous?" he said.
Secret Lover
Another theory is that Dando was murdered by someone she knew.
At the time of her death Dando was engaged to a doctor, Alan Farthing, an eminent gynaecologist who later delivered the Duchess of Cambridge's three children.
The couple had met on a blind date in 1997 and became engaged two months before she was murdered.
They were due to marry in September 1999.
Detectives wondered if there may be a secret motive involving revenge, money, sex, jealousy or a secret lover.
"They always say most people who are killed are killed by someone they know. You question everything and question everyone's motives in turn and think 'could they be the one who did it?'" her sister Judith told the documentary makers.
Alan Farthing married Dr Janet Stowell in 2008.