He wanted others to find children for him to sexually abuse, believing that to pay for such a service somehow legitimised it. And who better than to ask than prostitutes, he thought, with their loose morals and hunger for money?

Former garda sergeant Kieran O'Halloran (48) – sentenced to six years on Friday for attempting to pay prostitutes to find him young children for sex – was surprised but not shocked when gardaí knocked at his door in 2006.

It wasn't the first time. O'Halloran had been released from prison less than a year previously for the almost identical offence of attempting to pay prostitutes in exchange for access to children.

"He wasn't completely shocked to see us," said a garda source involved in the investigation. "During questioning, he seemed to realise the magnitude of what he was doing but felt a helplessness to do it. He was very placid and laid back."

O'Halloran, with addresses in Clane, Co Kildare, and Foxrock, Co Dublin, offered two prostitutes up to €10,000 in 2005 and 2006 to find him children as young as five, and asked one woman to organise "three or four children in a hotel room" for him to have sex with.

O'Halloran also requested a picture of a newborn baby with their genitals on view. Horrified, one of the prostitutes went to the gardaí, leading to his arrest. Through this woman, gardaí interviewed a series of prostitutes O'Halloran had slept with and discovered he had made the same request to a second woman.

It would seem, however, that nobody had been prepared to facilitate
O'Halloran's demand. "As much as we can be, we are satisfied that we spoke to all the prostitutes whose services he was accessing and that no one provided him with a child," the garda continued.

O'Halloran pleaded guilty to inciting the women "to organise or knowingly facilitate the use of a child for the purpose of sexual exploitation".

In court on Friday, he remained impassive as the judge read out his sentence and it would appear that he sought out children for sex with the same sense of detachment.

O'Halloran was previously married and he has one son. A member of An Garda Síochána for 22 years, he'd held a command post for 12 months in Croatia while working for the United Nations.

He had an "exemplary" record in his role but was forced to resign when the initial charges of attempting to pay for access to children came to light in 2001. After his arrest, his wife left him.

"He was well regarded and liked by his colleagues in Drogheda. Everyone was shocked when it first emerged, no one more so than his wife, I'd imagine," added the source.

The court also heard of sexual abuse O'Halloran himself had suffered when in boarding school and also of later abuse inflicted on him by a neighbour.

His defence counsel Lúan O'Braonáin SC insisted his client was indulging in "fantasy" by offering €10,000 for access to children because O'Halloran did not have that kind of cash and was on the dole. But others have privately commented that O'Halloran has some wealthy friends – and that he was able to afford visits to prostitutes.

None of O'Halloran's family was present in court but he is believed to have the support of his parents and siblings. He had been attending counselling at the Granada Institute, Shankill, Dublin, at the time of his most recent offences and he is now undergoing intensive therapy in prison.

As O'Halloran was led away in his smart suit on Friday, looking defeated and deflated, to begin his six-year sentence, Judge Katherine Delahunt's words were surely ringing in his ears.

"You've had ongoing treatment with the Granada Institute and the probation service," she said. "They've found you're still a very high risk of reoffending."