The discovery that one of this country's most notorious serial paedophile priests has been living under an assumed name within a Catholic church community in Holland is a chilling reminder of how cunning and manipulative such abusers can be. It is also a reason to review how well-supervised potentially dangerous abusers are when they are released from prison.

Fr Oliver O'Grady served seven years in the US for repeatedly raping two young brothers in their Californian parish. They were just two of as many as 40 children he sexually molested, one a nine-month-old baby. Every time he was discovered, his bishop moved him on to another parish. For that sin of omission, the diocese has had to pay record damages in America.

On release, he was deported to this country, but because he arrived here before the sex offenders' register was established, there are conflicting reports over whether he was put on it. Even so, gardaí try to keep tabs on him. They are not always effective. In the past, he was filmed for the documentary Deliver Us From Evil in the playground in Merrion Square. He lived close to a national school. His move to Rotterdam over a year-and-a-half ago saw him assume a name and identity as "Brother Francis". He volunteered at a women's shelter – full of vulnerable women and their children. He inveigled his way into a Catholic parish that, as our pictures show, meant he could indulge his fascination for children – even standing close to them at the baptism of his friends' baby.

The implications are enormous. We do not know whether O'Grady abused any children, or attempted to, while in Holland. He is now back in Ireland, having fled the country following a visit from Dutch police in February. He since returned to Holland briefly and was spotted wearing a fake beard at a station in Rotterdam on 14 April.

But his supervision, or lack of it, is alarming. Were Dutch police warned of the danger O'Grady posed? Did any of the priests in the parish where he helped out with mass, coached the choir and generally acted as a church warden, know of his background? People on the sex offenders' register are not allowed take any work that involves access to children.

Psychiatric reports for court cases in the US labelled this former priest a serial abuser who needs lifelong monitoring. It is clear that for the past 18 months, that monitoring has been defective.

Whether O'Grady is on the sex offenders' register or not, his behaviour is a cause for major concern. Ways of ensuring that O'Grady, and men like him, have no contact with families and children need to be rigorously enforced.