Irish police have detailed how the search and subsequent investigation into the murder of Ana Kriegel was “unprecedented and innovative”.

Speaking following the sentencing of two 15 year-old boys, known as Boy A and Boy B, for the schoolgirl’s murder on Tuesday, Superintendent Mark Gordon said: “It was unprecedented, and please God we never have an incident of this type again in this jurisdiction or anywhere else.

“This case by its very nature was unprecedented in the history of our jurisdiction, and now the youngest children ever convicted of the heinous crime of murder in our time.”

Ana’s parents first alerted police when their daughter had failed to come home after leaving with Boy B on May 14 2018.

Officers from nearby Lucan Station were brought into the investigation after Ana had been missing for 18 hours, in which time searches had begun, both boys had been informally interviewed and a trace placed on Ana’s mobile phone.

“From the time we became made aware, it was obvious something was seriously awry,” said Mr Gordon, who was based at Lucan Garda Station at the time of the incident.

“It was obvious this was above and beyond for a normal missing child incident. Usually when children go missing they come back within an hour.”

What followed was a three-day search for the schoolgirl and subsequent murder investigation involving the National Bureau of Criminal Investigation, the Garda Technical Bureau, the Cybercrime Bureau and the Irish civil defence forces.

Some 500 lines of inquiry were investigated, more than 500 statements were taken, 250 exhibits were seized and examined, and nearly 700 hours of CCTV had been watched.

When the boys, then aged 13, were nominated as formal suspects, Mr Gordon said that the force had gone to great lengths and implemented “special arrangements” to ensure the boys were made comfortable and their rights protected at all times.

This was due to “their vulnerable age”, and Gardai feared anything less could have resulted in allegations of inappropriate or oppressive behaviour towards two 13-year-olds, who were only at that time suspects.

“We availed of any chance to mitigate any probable lines of defence and to ensure the rights of the boys were vindicated to the highest degree,” Mr Gordon added.

For instance, rental cars were used when visiting the homes of the boys, instead of unmarked police cars, and evidence was taken from their houses in black bin bags, as opposed to standard evidence bags, to not arouse suspicion from onlookers.

“The idea behind this was to preserve the anonymity of the boys and of their families,” Mr Gordon added.

Instead of being held in cells, offices inside two separate police stations which had been cleared out of all staff and unnecessary personnel, had beds and other furniture placed inside, and each boy was accompanied by one parent at all times.

Detective Inspector Mark O’Neill was appointed senior investigating officer (SIO) in the case at an early stage, which was unusual within Irish police protocols. However, the level of concern at the time led superior officers to believe it was warranted.

Mr O’Neill said the interviews with the boys were “meticulously planned” and conducted by highly trained interviewing officers, whose interview style is “not designed to elicit confessions, it is designed to establish what the truth is”.

Throughout these interviews both boys lied about their whereabouts and knowledge of what happened in the incident, before Boy B eventually admitted to officers he had seen Boy A attack Ana.

“Given the amount of evidence which came to light in this case, there was considerable thought and planning went into how that evidence was going to be utilised in interviews to have the best chance of establishing the truth of what occurred,” Mr O’Neill added.

“That planning took place over a period of days, and I think the effect was evident in the trial.”

Concluding, Mr Gordon said that any officer who had worked on the case had been affected and changed by the experience.

“The impact on officers in cases of this nature can at times be considerable, so we’re very clear about our requirements to mind ourselves and our people,” he said.

“We all have a duty of care to our young people and juveniles, it’s certainly something that we didn’t anticipate, but we now need all to mindful of the capacity of people to offend in this way.”