- What are the Babes in the Wood murders?

The Babes in the Wood moniker, inspired by the popular fairytale and pantomime, was coined by the Press to describe how nine-year-olds Nicola Fellows and Karen Hadaway were found huddled together in a woodland den.

It emerged in the retrial that the 18-year-olds who found the girls never actually saw the bodies and made up the description, partly to provide comfort to their families.

- Why was Russell Bishop a suspect in the original investigation?

Bishop, then aged 20, knew both victims and was seen in the area on the night they disappeared. He lied to police and described details only the killer would know.

A blue Pinto sweatshirt he discarded en route home was linked to Bishop and the murder scene and identified by his partner Jennifer Johnson.

- What went wrong in 1987?

The prosecution relied on the time of death being before 6.30pm, yet witnesses saw the girls eating chips around that time and potato was found in Nicola's stomach.

An expert could not confirm that fibres on Bishop's clothes could only have come from the Pinto or it was definitely worn by the killer.

Nigel Pilkington, of CPS South East, said: "Back in 1987 the difficulty with the case was to say Russell Bishop was wearing a Pinto sweatshirt. We had little bits of evidence to say he was wearing that sweatshirt, including evidence from his partner Jennifer Johnson who regrettably changed her mind in the witness box and that caused us some difficulty."

Detective Superintendent Jeff Riley added: "I'm not clear why they went for that 6.30pm time frame. We certainly would not. The issues with any investigation is people can be quite vague around times."

- What did the then trial judge say about it?

The Pinto sweatshirt evidence was limited to fibres and ivy hair, which the trial judge said was "not very much" by way of evidence concerning the "commonness of fibres".

He said: "If you are not sure that Mr Bishop wore that Pinto that night, you will acquit, will you not?

"If you are not sure that those girls were killed between 5.20pm and 6.30pm you, according to the defence, acquit."

- What happened after Bishop was acquitted?

Bishop faced hostility from the local community, which led him to consider suicide, taking his children to Beachy Head before changing his mind.

He was jailed for life for the kidnap, sexual assault and attempted murder of a seven-year-old girl at Devils Dyke on the South Downs on February 4, 1990.

Meanwhile, Nicola and Karen's parents campaigned for a change in the law.

- What is double jeopardy?

In 2003, Parliament changed the law to allow acquitted defendants to face trial again if there was "new and compelling evidence".

Mr Pilkington said it was "very rare", with only around 20 cases.

- Are there other similar cases?

In 2006, Billy Dunlop, then 43, made legal history when he pleaded guilty to the 1989 murder of Julie Hogg, from Billingham, Teesside, having confessed to a prison officer.

Three years later, Mario Celaire, a footballer with a history of violence against women, was given two life sentences after admitting killing his ex-girlfriend seven years after being cleared of the crime.

In 2010, new forensic evidence led to the conviction of loner Mark Weston for the 1995 murder of Vikki Thompson, for which he was originally cleared.

The most famous double jeopardy case was the 1993 racist murder of Stephen Lawrence, which finally led to the conviction in 2012 of Gary Dobson and David Norris.

- How does the Bishop trial compare?

It is believed the Babes in the Wood incident is the oldest double jeopardy case to come to trial, and one of the most controversial.

Mr Pilkington said: "The previous acquittal was subject to a great deal of publicity and discussion and obviously the death of two nine-year-old girls is always going to remain in the public eye. At least in the Brighton area. So it's been in the public consciousness for 32 years."

- What was the new and compelling evidence?

New scientific evidence included a "one in a billion" DNA match to Bishop on the Pinto sweatshirt and on Karen Hadaway's left forearm.

Mr Pilkington said the DNA on Karen meant Bishop "touched her arm and he can only have touched it at the murder scene".

- How did Russell Bishop respond?

Bishop tailored his defence to counter the "incontrovertible" evidence, by claiming he touched the girls' bodies to feel for a pulse.

Mr Pilkington added: "Why does he say he took the pulse on the neck on Nicola? Because there is a red paint fleck from his jumper. It's pretty preposterous.

"He does not dispute it is his DNA, he can't. What he says is it has been contaminated. But it's pretty weak stuff, we would say."

- How else did the 2018 trial differ?

The prosecution abandoned the narrow time frame and did not call Ms Johnson but instead pointed out similarities between the murders and the 1990 assault.

In turn, Bishop cast suspicion on Nicola's father Barrie Fellows.

- Was there any truth in the allegations against Mr Fellows?

No, says Mr Pilkington, who said it was an "outrageous slur" and "completely without foundation".

- Can Sussex Police or the justice system be held responsible for Bishop being free to attack again in 1990?

Mr Riley acknowledged the families were "very angry" in 1987 but insisted the original investigation was "professionally led" and was "thorough".

Mr Pilkington said the DNA evidence transformed what was a "difficult" and "mainly circumstantial case".

He said: "We do not convict people, neither do the police. We understand from the perspective of the family of the seven-year-old girl how appalling that must seem to them but beyond that I cannot say."

- How did the families react in court, particularly to the allegation against Mr Fellows in the retrial?

Mr Pilkington paid tribute to family members in court, saying: "They have had so much thrown at them, their resilience is astonishing to see."

- What about the 1990 victim?

Mr Riley said: "We continue to provide support to her to this day. She is obviously having to relive the whole thing again because of the interest in this trial."