I have worked with men who have abducted and killed children. Often, their capture has failed to save the child and has not come about through good police work. 

The planning needed to take the child can not be overestimated. It was clear from the beginning in Portugal that we were dealing with an abduction and the need to "think offender" was essential. 

What was his motivation? How would he initiate contact and target the child? How would he control the environment to evade discovery? 

Portuguese police cannot ignore the UK's experience in such cases. In the early '90s a British paedophile group filmed the sexual abuse of Portuguese boys. 

 At one stage the Americans were so concerned about the role of British paedophiles in Portugal that I was approached about the targeting of schools there. International co-operation should be part of police thinking

However, there is no culture of community policing in Portugal and they have laws that prevent the discussion of cases. This is clearly the wrong way round. The media are essential in passing co-ordinated and directed information to the community. 

 In this case, speculation is rife, confused messages are likely to be given.

 The parents will be feeling guilty for leaving the children and even a half hour is a long time if a child wakes up and starts to cry immediately after one leaves the room.

This could, possibly, lead to a woman on her own, who has lost a child, saying to herself wrongly that the parents did not care for this child and deciding to take the girl home. No paedophile, no conspiracy - just a lonely woman.

The window of opportunity for the abductor means that the information given by the parents has to be very accurate. Police must help them to say exactly how long it was since they last saw their child.

 The parents need to know that if this was an offender who planned the abduction then there is probably nothing they could have done.

I once asked an abductor who had killed girls how we could stop him. He said: "I suppose you would have to chain a child to the mother." But he added: "No, that would not work. I would take both."

Ray Wyre is an expert in sexual crime who worked in the UK Probation Service in the 1970s before specialising in programmes for sex offenders.