Nikki Allan's mother Sharon Henderson says errors in the police investigation into her daughter's murder have caused her "30 years of heartache."
Northumbria Police fixated on neighbour George Heron, while glaring pointers to David Boyd's guilt were never investigated.
A litany of oversights meant Boyd did not become a suspect until 2017 when Sharon pressed Northumbria Police to reinvestigate the case with new eyes.
Read more: Video shows moment Nikki Allan Sunderland murder accused is arrested
A combination of her determination, diligent police work by the new team and advances in DNA technology meant that Boyd was arrested for the first time in 2018.
Sharon, 55, said: "I was so badly let down by the police, they had so many chances to catch Boyd years and years ago.
"Instead I have spent 30 years investigating Nikki's death myself and I could have been spared that if the police had done their job properly.
"I first mentioned that they should look at Boyd's house in 2013, but nothing ever came of it until years later.
"I was treated like a drunken mother with mental health problems, I never felt listened to by the police.
"To hear everything they missed or failed to investigate has been devastating."
Read more: Man accused of murdering Nikki Allan ‘admits fantasies of young girls'
Boyd was interviewed as a witness, happily making a statement to officers in the knowledge that an innocent man, 25-year-old Heron, was their prime suspect.
The original investigation, led by Detective Superintendent George Sinclair, now deceased, failed to pick up on Boyd's two previous convictions at the time Nikki was murdered.
In 1986 he was convicted of causing a breach of the peace by approaching a group of young children aged between eight and ten in Sacriston, County Durham.
He seized one girl by the arm and asked her for a kiss, warning them not to say anything before he left.
He had a further conviction, also from 1986, for indecent exposure against an adult woman who was out jogging when he encountered her.
Boyd lived three doors away from Sharon's father Dickie Prest and step-mother Jenny Prest and he knew the family.
His partner Caroline Branton Sr was a babysitter for Nikki and her three sisters and Nikki had occasionally spent time at the flat she and Boyd shared in Sunderland's Wear Garth housing complex.
It meant she was comfortable enough with him to follow him away from Wear Garth, skipping happily behind him to her death at the Old Exchange Building, a derelict warehouse on the city docks.
In the statement taken from Boyd he was identified as the last adult male to see Nikki alive by his own admission and he still was not treated as a suspect.
A young boy from the estate told police he had been in the building where Nikki's body was found with Boyd the previous Sunday, just three days before the murder on 7 October 1992.
Read next:
* Nikki Allan murder trial jury hears of find of new DNA evidence
* Nikki Allan: Jury in David Boyd murder trial told how body was found
* Nikki Allan: Jurors see photos and sketches of suspect David Boyd
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Boyd explained that he and the youngster, who was 12, had been looking
for wood to build a pigeon hut.
But he admitted he knew the building and how to enter it via a boarded up entrance at the back.
As years went on, Boyd continued to offend but there was no cross referencing between his child sex offences and the murder of Nikki - even after he confessed to a sexual interest in young girls at the relevant time.
In 1997 he exposed himself to three young girls in a park, one of whom he knew.
He told police he did not know why he had done it.
Then in 1999 he approached two girls aged nine and 12 in Primrose Hill
Park in Stockton on Tees.
He sexually assaulted the younger girl and was convicted the following year.
Boyd was spoken to by probation worker Gillian Dixon, who was compiling a pre-sentence report, and told her: "I would think about young girls being naked,
touching their body and having intercourse with them."
He said it was "a phase" he went through when he was aged around 22.
At the time of Nikki's murder Boyd was 25 but no connection was made between him and her murder after his disclosures.
Meanwhile, the police continued to press on with George Heron as their only suspect.
He was charged with murder and appeared for trial at Leeds Crown Court the following year.
However the case was halted by the trial judge, Mr Justice Mitchell, after he heard the police interviews of Heron, which lasted three days.
He ruled the interviews were "oppressive" and that Heron was hectored into making a confession to something he knew little or nothing about.
The judge said that the police had misrepresented evidence in their interviews with Mr Heron.
He said that two witnesses had given police descriptions of a man and there were striking differences between them.
Neither witness was able to pick out Mr Heron in an identity parade.
He went on to criticise the police methods of questioning, saying that their manner was 'oppressive' as they told the accused that they believed he was the killer despite his constant denials.
Heron was cleared at the judge's direction but his life was ruined.
He was first to leave his family behind in Sunderland and move away under an assumed name, first to the south of England and then to Ireland.
He was described by the prosecution in Boyd's trial as "an innocent man."
In his police interview Mr Heron guessed at what officers wanted him to say, offering answers, only to be corrected with "howay George" said repeatedly by the interviewing officers.
One section of the interview tape reads like this:-
Heron: “picked up the nearest thing and hit her with it.”
Detective: “and what was that?”
Heron: “a brick”
Detective: “where did you hit her George?”
Heron: “on the head.”
Detective: “how many times can you remember?”
Heron: “no”
Detective: “how many times do you think?”
Heron: “I lost count”
Detective: “that’s not all you did George is it? Howay you have told us the truth we are just about there George we are nearly finished alright. Did the brick knock her out George?”
Heron: “there was blood”
Detective: “did that kill her George with the brick? George it didn’t
did it George?” There’s more isn’t there George?”
“Howay you have told us there was blood all over the place what else did you do. George we know what’s happened, we know what’s happened, so you know you are not holding anything back by not telling us, George, what else did you do?”
“George howay son, just finish it off and tell us what else you did. George …”
Heron: “went to throttle her”
Detective: “you went to throttle her, what with?”
Heron: “me hands”
Detective: “but you hit her with something else didn’t you George?”
Heron: “don’t remember”
Detective: “George, think, I know it’s not very nice son, but just think what did you hit her with. Eh George?”
Heron: “fist”
Detective: “what else? Howay George you used something else didn’t you? George we know, howay George what else did you do? Come on.”
Heron: “piece of metal”.
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