Child killer David Boyd was wearing a T-shirt which said “I am unstoppable” during one of his police interviews and for almost 30 years he must have thought he was.

Between battering and stabbing to death his seven-year-old neighbour Nikki Allan in 1992 and police first arresting him on suspicion of her murder in 2018, he must have thought he had got away with it scot-free.

After initial denials, one of the first comments topless Boyd made after answering the door to detectives was: “What evidence have you got?”

Read more: Video shows moment Nikki Allan Sunderland murder accused is arrested

Prosecutors said this was not the reaction of an innocent man, wrongly accused of killing a little girl almost 30 years before, and he must have known the net was closing.

Boyd, also known as Bell or Smith, had seen another man stand trial for her murder in 1993, although he was subsequently cleared on the directions of the judge.

Police wrongly believed the innocent man was guilty and for some years insisted they were not looking for anyone else in connection with the murder.

Boyd was free to continue with his life and in 1999 he committed an indecent assault after approaching young girls in a Teesside park and grabbing one of them, who was aged just nine.

Read more: Man accused of murdering Nikki Allan ‘admits fantasies of young girls'

He was caught and was jailed for 18 months.

Tellingly, Boyd was to confess to a probation officer how he had previously had sexual fantasies about naked “young girls” when he was in his early 20s.

Boyd was 25 when he murdered Nikki.

The jury was told about Boyd’s 1999 conviction for indecent assault and a breach of the peace in 1986 when he approached a group of children and asked for a kiss.

The jury was not told about two flashing offences he committed in 1986 and 1997.

Born in London to a father who was in the British Army, Boyd went to a school for pupils with behavioural problems when he was 14.

Aged 17, he went to a Barnardo’s home on Tyneside and later a resettlement unit in Chester-le-Street, County Durham.

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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He relocated to the run-down Garths flats in Sunderland and moved in with Caroline Branton, an older woman who had an adult daughter, and his partner’s 11-year-old son who hated him.

Ms Branton regularly babysat for Nikki’s family and so Boyd knew the little girl.

In later years he moved to Teesside, never settling down with a family and never getting a job.