Nikki was lured to her death on Oct 7 1992 by Boyd, who then used the name Smith or Bell.
She had been playing close to her home in a block of flats in Hendon in the dockland area of Sunderland,
She knew Boyd because his girlfriend, Carolin Branton, sometimes babysat for her and her three sisters, so she happily skipped behind him as he led her away from home.
Boyd then assaulted Nikki outside the Old Exchange Building, a derelict warehouse on the River Wear, causing her to let out a scream which was heard by passers-by.
He pushed her through a boarded-up doorway and carried out a frenzied assault before dragging her body by the ankles down a flight of steps into the building’s basement.
Nikki was found the next day by locals, who had formed search parties, resting against a wall in a dark corner of the building. Her body was at first mistaken for “a bundle of rags”.
Local man Mr Heron was quickly identified as the main suspect and went on trial at Leeds Crown Court.
Even after he was acquitted, Northumbria Police issued a statement saying they were not looking for anyone else.
Mr Heron was forced to leave his family behind in Sunderland and move away under an assumed name, first to the south of England and then to Ireland.
It later emerged that the original investigation, led by Detective Superintendent George Sinclair, now deceased, had 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 10 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.
Boyd continued to offend
He had a further conviction, also from 1986, for indecent exposure when he jogged past a woman three times while naked from the waist down.
As the years passed, 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 didn’t 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 in 2000.
After Boyd’s conviction Northumbria Police issued an apology to Mr Heron and to Ms Henderson.
Ms Henderson rejected the apology, describing it as “hollow”, adding: “I am 57 years old now. I have spent over 30 years fighting for justice. My life and that of my family has never been the same since Nikki was murdered.
“By murdering Nikki David Boyd has destroyed not only Nikki’s life – the life of my beautiful daughter – but my life and the lives of my daughters and grandchildren. We have not been able to live normal lives since that day.”
Nikki’s father David Allan said in his statement, said: “From that night, the 7th of October 1992, my life changed. I am and forever will be affected by her death and the manner in which she died.
“I have feelings of anger and hatred and I will never be able to forgive the man responsible.”
In a statement read outside Newcastle Crown Court on behalf of Ms Henderson, Harriet Wistrich, director at the Centre for Women’s Justice, said: “Sharon Henderson was 25 at the time her beautiful seven-year-old daughter Nikki was murdered by David Boyd. She is now 56.
“She thanks the efforts of all those involved in bringing the murderer to justice and welcomes the sentence handed down today in court to the man who so brutally took Nikki’s life, and in doing so caused irrevocable damage to Sharon and all her family.
“Quite rightly, the gravity of the sentence passed today reflects Boyd’s refusal to plead guilty, which meant that Sharon and family members had to endure hearing details of the horrific murder at trial a second time around.
“This, however, is not the end of her campaign for justice. Now, Sharon demands that Northumbria Police are held accountable for their historic failures that allowed a 31-year wait until the right man was convicted.
“The full extent of the failures remain unknown and therefore we are demanding a public inquiry to examine the historical investigation which led to the wrong man being prosecuted and the police failing to consider alternative suspects until over 20 years later.
“We are also preparing a complaint to be lodged with the Independent Office of Police Complaints and exploring a civil claim for damages on Sharon’s behalf.”