In a trial that laid bare the most horrific facets of his murderous past, Robert Black never betrayed one flicker of emotion.

Arms often folded, sometimes yawning, occasionally raising his eyes to the ceiling, the killer was an unwavering picture of cold indifference.

For a man who denied murdering little Jennifer Cardy, as he had when accused of killing his three other victims, there was not even the attempt to conjure the faux visage of an innocent man.

Not that he wasn't listening from the dock of Armagh Crown Court. The balding 64-year-old, now an ageing shadow of his menacing mugshot of 20 years ago, asked for his specialised hearing device to be replaced a number of times.

Almost everyone else in Court No 1 wished they could shield their ears from the gruesome deeds of one of the UK's most infamous serial killers.

Black was born in 1947 near Falkirk in Scotland to single mother Jesse Hunter Black. The factory worker put her son up to be fostered within weeks.

The couple that took him in - the Tulips - were in their 50s and lived in Kinlochleven in the West Highlands.

Within 11 years both had died and Black was placed in a children's home back in Falkirk.

He claims his desire to self-abuse and his fascination with the genitalia of young girls had already developed well before then.

"I'd like to know where it came from," he told police years later.

"I've got the two unfortunate distinctions now - I'm attracted to young girls and I abuse myself.

"Someone once said to me, a so-called doctor, that it had to be a learned behaviour. Something that had to be taught.

"Well, I have no recollection, but then I don't remember nothing before my first day at school, as a five-year-old."

In Falkirk his proclivity for sexual violence emerged when, as a 12-year-old, he was accused of trying to rape a young girl. No charges came of it, but Black was moved to an all-boys' home in Musselburgh as a result.

In that institution he claims he was the victim of sexual abuse at the hands of a male staff member.

When in Musselburgh he would walk the short distance to Portobello to swim and work as a lifeguard at the coastal resort's swimming pools.

Twenty years later little Caroline Hogg would disappear close to those same pools.

When he turned 15, Black left the home in Musselburgh and moved west again, to Greenock outside Glasgow.

A year later, in 1963, he faced the courts for the first time after molesting a seven-year-old girl in an abandoned air raid shelter.

He had lured her from a swing park with the promise of showing her a box of kittens. Instead he choked her to within an inch of her life and then violated her. He left her there in the darkness, lying unconscious.

Yet he was not incarcerated for the crime, receiving only a caution for lewd and libidinous behaviour.

Black relocated back to Falkirk where he started dating his one and only girlfriend. They stayed together for a while and Black even asked her to marry him. She said no and the relationship ended acrimoniously.

He harboured immense bitterness over the rejection from then on. After he was charged with the three murders in 1992, he reportedly told officers to tell his ex-girlfriend "She's not responsible for this".

Three years after attacking the girl in Greenock, and now working as a builder back in Kinlochleven, he was not so lucky with authorities after being reported for abusing the daughter of a couple he was lodging with.

In 1967 he was found guilty of three counts of indecent assault and sent to borstal in Polmont outside Falkirk for a year.

"I did not like getting locked up and vowed I'd never get locked up again," he later told police of the experience.

Black moved to London on his release and soon became immersed in the sordid world of under-the-counter child pornography.

Again he found work as a swimming pool attendant, where he could earn money while spying on young girls in their costumes.

Swimsuits were one of the paedophile's particular fetishes and behind the locked door of his rented room in north London he would squeeze himself into young girls' costumes and act out sordid sex acts.

A one-piece suit found in his van when he was finally captured in Stow in 1990 was sized to fit ages eight to 10.

"I would have thought that was for a larger child than that," he replied matter of factly when confronted by police.

"Cause I know I could get it on and I'm no nymph."

His lust for harder-core child porn took him on shopping trips to Copenhagen and then to Amsterdam.

Around this time he also obtained his driving licence, enabling him to secure a job with Poster, Dispatch and Storage Ltd, a London-based delivery firm owned by a Norwegian couple, in 1976.

In retrospect, this job turned out to be his means to facilitate his murderous reign. Delivering posters throughout the UK for more than a decade, he was able to stalk the country as an anonymous van driver.

The back of his van became a lair where he would abuse himself and his victims with a vile stash of crudely-fashioned instruments.

A delivery run took him past Coldstream in 1982 when he snatched Susan Maxwell, back to Portobello a year later when he stole Caroline Hogg from the promenade, and through Leeds in 1986 when he abducted Sarah Harper.

Robert Black would probably never have set foot in Northern Ireland in August 1981 if he had not been sent there to deliver posters for the start of new beer and cigarette campaigns.

But ultimately his job also proved his undoing. No other serial killer could be so meticulously tracked in years to come with the use of old work records and petrol purchase receipts.

When Black casually scribbled his name at the bottom of a credit card docket after filling up in the hours after his latest killing, little did he know he was as good as signing his own confession.

Since being caught red-handed in Stow, with a barely conscious victim hooded and gagged in the back of his Ford Transit, he has insisted that was his only "slip" - the only time he ever kidnapped a young girl in his van.

Bizarrely, Black would admit to doing much more in his fantasies.

He told officers he dreamed of abducting young girls and abusing them in the back of his van while at work.

He even admitted that in his fantasy he would take the children to laybys - all Black's murder victims were ultimately dumped at or close to laybys.

Some of his supposed make-believe settings also bore a striking comparison with the actual scenes of his crimes.

None more so than the quiet country road where Jennifer Cardy was dragged from her bike.

Black's fantasy of a tree-lined road sweeping down a hill and round a gentle bend, with a house set back on one side, might as well have been an exact description of the spot on the Crumlin Road where the nine-year-old vanished.

The killer told detectives he was averse to analysing these fantasies.

"And is there any particular reason why?" an officer asked.

"I don't know, maybe because I'm not exactly proud of the way I feel towards young girls," he replied.

"Like there's a part of me that knows I'm wrong, that knows that it's wrong, that I shouldn't be doing things like that, I shouldn't even be thinking things like that, but there's the other part that says 'you like it, go on'."

He called this dark half of his personality his "offending side".

But he has always insisted these dreams were only figments of his imagination.

Why he would admit to even dreaming about such things, when being accused of murder, is a question only he knows the answer to.

The Crown believed it was a coded confession - a boastful and arrogant man playing cat and mouse with the police, teasing them with hints but stopping before he said too much.

It was a dangerous strategy and one that ultimately failed.

The jury members saw right through his denials.

But as Black was led from the dock, they, like everyone else, could only wonder what other secrets lie hidden behind that soulless mask.

Victims: Jennifer Cardy and Black's Scottish targets

Evidence: the crucial petrol receipt

The lawyer: ending unfinished business

Robert Black guilty of fourth child murder