The strategy police deployed when questioning Robert Black over Jennifer Cardy's murder took a year to plan, officers involved have revealed.
The approach the Police Service of Northern Ireland (PSNI) took to tease out information from the serial child killer was formulated with the help of a specialist clinical psychologist and experienced detectives from other forces.
The PSNI's serious crime custody suite in Antrim was completely cleared for the three days of interviews with the notorious Scottish paedophile in May 2005.
"Black was the only prisoner," explained detective superintendent Raymond Murray, the officer who led the Cardy case.
"People were told if you have planned arrests please put them back slightly or bring them forward because these three days we are emptying the whole place and we took over - we used all monitoring rooms, we used all facilities."
Poignantly but entirely co-incidentally, the first interview was held on May 16 - Jennifer's birthday.
Black had been transported from prison in Wakefield in Yorkshire where he was already serving life for three child murders and other offences against young girls.
Officers from the PSNI's forebear, the Royal Ulster Constabulary, had quizzed Black in 1996 but he had not revealed enough to prompt charges.
Mr Murray re-opened the cold case in 2002 and was able to source some crucial circumstantial evidence that placed Black, a London-based delivery driver at the time, in Northern Ireland on the day of the murder.
So in 2004, Mr Murray and experienced colleague detective chief inspector Stephen Clarke started planning to once again question Black under caution.
"The interview strategy took a calendar year to plan," explained Mr Murray.
At the time the PSNI was working jointly with detectives from Devon and Cornwall police investigating the 1978 disappearance of schoolgirl Genette Tate.
Devon officers interviewed Black first, but the PSNI heard and watched every second of it.
"We sat in the other room and watched for two days, I am not convinced he knew we were there," said Mr Murray.
"The army have a saying, 'time spent on reconnaissance is rarely wasted', and that really, really helped us because we thought he'll talk, he'll talk if we plan this right, we can get a lot of material here."
He added: "We watched very, very carefully. We had a clinical psychologist watching too, we had Roger Orr (a Scottish detective who quizzed Black in 1990) watching as well because Roger at that stage probably knew him the best.
"We all sat in a very small room and watched for two days and he is a fascinating character Mr Black and we took their experience, re-drafted our interview strategy and then we went."
Devon and Cornwall police completed the first phase of their interviews - dealing with non-contested facts - during those two days.
At that point the PSNI took the lead, deciding to go through all the phases right up to confronting the killer with Jennifer's murder.
But getting to that end-game was deliberately going to take a long time.
The officers knew that Black went into his shell when accused directly, he also recoiled from words like "murder" and "killer", so detectives steered well clear of any of that as they tried to get the predatory paedophile to open up.
Mr Clarke, who is now retired but came back as a PSNI consultant to see the case through trial, explained the thinking.
"Part of the work around planning the interviews was trying to understand him," he said.
"And I accept that you will never understand him but you can put in place certain measures that will make him respond and tick and the likes of the word 'murder', I don't know whether people noticed but whenever they said 'murder' in court he took his (specialist hearing) earphones off, he can't cope with that word 'murder' - so the earphones came off and were sat down."
The PSNI deliberately chose a man and woman interviewing team, just in case Black favoured one over the other.
Detective Sergeant Patrick McAnespie was the senior officer along with Detective Constable Pamela Simpson.
But it soon became clear Mr McAnespie would have to take a back seat.
Mr Murray, who was watching from elsewhere hidden from view, explained what happened during the first post interview debrief.
"We said 'Pat, don't speak for the next two or three days, he doesn't like you," he said.
"And he was very, very good and you've no idea how important that is and he had the discipline just to act - he was the senior officer in the interview room - he drops back and just lets Pamela Simpson take the whole thing for three days.
"It was very, very tight on her and exhausting interviewing him for three days."
Dc Simpson, an experienced detective in child abuse cases, appeared to put Black at ease and he started talking freely.
But he got upset when the female officer claimed that sex toys were found in his van when he was caught red-handed in the Scottish village of Stow in 1990 with a barely alive six-year-old girl in the back.
That hitch was discussed during the next debrief.
Mr Murray explained: "We said, 'right, what are we going to do here?' and we said 'go in and apologise'.
"And she did, no problem, 'sorry about that, I got that wrong'. And he just all of a sudden came back on the rails with her again and off they went again."
Those same exchanges between Dc Simpson and Black would be played to the court six years on during his trial for Jennifer's murder.
During this phase of questioning, Black conceded to being in Northern Ireland on the day of the murder - a crucial breakthrough for the investigation.
Though, as Mr Clarke pointed out, Dc Simpson made sure to ask did he "accept" being in Northern Ireland, not did he "admit" to being there.
"He doesn't like the word 'admit' and that's why you heard a lot in the interviews 'do you accept?'," he explained.
Though the acceptance of being in Northern Ireland was key, officers did not expect what they would get next.
Black, cajoled by Dc Simpson, began to outline his recurring sexual fantasy of abducting young girls.
Maintaining he had never murdered anyone in reality, the vivid and sordid details about his dreams bore a remarkable resemblance to his crimes.
Taking a girl away in his van, perhaps from a quiet country road, driving somewhere safe, perhaps a roadside lay-by, and then abusing the girl in the back.
It was disgusting stuff, but detectives Simpson and McAnespie let him divest himself of it all.
They did not spot it immediately but after reviewing the tapes the investigation team realised Black had effectively admitted to doing in his fantasy exactly what they believed he had done to Jennifer in August 1981.
His description of a quiet country road sweeping down a hill and turning round to the left, flanked by high hedges and with one house set back from the road, was almost a perfect description of the spot on the Crumlin Road in Ballinderry where the nine-year-old was snatched.
"The irony was we never expected to get a confession," said Mr Murray.
"We did get a confession at the end of the day, it just took us a while to recognise it."
When the time came to confront Black with the allegations of kidnapping and murdering Jennifer, Ds McAnespie stepped back into the frame.
But as expected Black just clammed up, refusing to admit anything.
"In the last interview I think he realised, I strongly believe he realised 'I've messed up here, I've gone too far, I've said too much'," said Mr Clarke.
For the PSNI team, however, he had already admitted plenty.
Mr Murray revealed that Jennifer's father Andy was sure Black would confess during questioning.
"Andy said to us 'you will get a confession' and we said 'Andy, no we won't, it's not in him to confess' and he said 'no, I'm telling you now', and obviously his faith was at work there too, and we were trying to manage his expectations.
"Now on reflection he did give a confession, we just didn't recognise it at the time."
He added: "I would say it is the best interview that I have ever been involved with - it worked superbly."
Both Mr Murray and Mr Clarke, who worked together on the case for 10 years, are unequivocal when asked if the eventual conviction was the most satisfying of their careers.
"No question," said Mr Murray.
"Absolutely," added his long time friend and colleague.
"To take what we had, develop it to what we did, and present it the way we did - from a professional point of view there's no doubt it doesn't get any better."