This would severely hamper his carefully constructed plan to grab a child from the street and take her back to his flat.
He did not know when he would get another chance, and cruising round a South Coast town shortly before 9am on Tuesday, 19 January, he was feeling increasingly desperate.
Then he saw them. Two little girls on their way to school, bags over their shoulders, laughing and joking with the shared complicity of 10- year-olds. The street was narrow and they were walking in the road. Hopkinson stopped the car, jumped out and one of the girls asked him the time.
He grabbed them both and forced them into the boot of the turquoise Vauxhall Corsa, so quickly they didn't even scream. Astonishingly, no one else saw what had happened.
Later that afternoon he carried the children one at a time up to his flat in a large black sports bag. Two weeks earlier, Sussex Police had visited him as they had the previous year, but without evidence all they could do was warn him and say it was inappropriate to entertain young children in his flat.
But as Detective Superintendent Jeremy Paine was telling a packed press conference the following morning that he suspected the girls may have run away, fellow officers in Eastbourne were gathering evidence against Hopkinson and preparing to have him listed on the sex offenders register after a complaint by a child.
But, almost incredibly, officers did not liaise with each other. At that stage no one suspected Hopkinson of abduction. He was outside the five-mile radius in which kidnappers usually operate.
"I was fairly sure when we gave the press conference on the Wednesday morning that they would have been found by the afternoon," Mr Paine said.
By that evening there were more than 300 police searching for them as well as 50 Gurkhas and military police from nearby barracks. As the search was extended, detectives were checking the list of registered sex offenders.
"We had to prioritise and we had 500 houses in the block between the school and their homes," said Mr Paine. There were 100 people with convictions of assault and 36 people on the sex offenders register in the area. They all had to be checked before the search was widened to other towns.
"At that stage abduction was not the strongest theory and there had been a lot of reported sightings," said Mr Paine.
Detective Sergeant Doug Bick, head of Eastbourne child protection unit was at home in Hastings when he finally remembered Hopkinson and the investigation for which they had planned an arrest. DS Bick rang in and suggested they arrest him on the Friday morning.
He and Detective Constable Martin Toft, with three uniformed policemen, went to Hopkinson's flat and Hopkinson said he had to get dressed and asked them to return later. But he eventually let them in. The girls were sitting on a single bed in front of the television in the lounge. There were no handles on their side of the door.
DS Bick said: "His activities were being monitored as best we could but until he commits an offence all we can do is monitor. He is not the only paedophile who has abducted a child and it happened a long way from where he was living. Yes, he did have a previous conviction for abduction but in the absence of any specific intelligence that the children were there we acted as quickly as we could have done."
Mr Paine says his team conducted the investigation correctly. "We were right in what we did. We had to prioritise our search and you have to search a premises properly if you are going to do it at all.
"The lesson we have learnt is that in future we could send out the child protection teams to knock on doors in nearby towns straightaway."
ALAN HOPKINSON was able to operate undetected for so long because of a legal loophole. The 1997 Sex Offenders Act requires anyone convicted of a sexual offence against children to register with the local police and inform them when they move. The act is designed to allow the police both to monitor known paedophiles in their area and - in exceptional cases - to inform local people or organisations of their presence if they believe there is a genuine danger. But the legislation is not retrospective. Only people convicted on or after 1 September 1997 have to register with the police.
In Hopkinson's case dates are largely academic. Although his previous crime involved the kidnapping and imprisonment of a girl aged 11, he was convicted of non-sexual crimes. As a result, although police had their suspicions about him, he was not considered a "child-sex offender".
But after his release from prison, police became concerned when they had several complaints and tip-offs about his contact with young children, Hopkinson was warned in January 1998 that his behaviour was inappropriate.
When that failed to stop him, police and social services carried out another inquiry with the intention of securing a court order under the Crime and Disorder Act, passed at the end of 1998. This would have involved a magistrate issuing an order restraining him from having contact with children. He would have been the first person to have such an order imposed.
As it transpired, Hopkinson struck again while this inquiry was in progress. Police will have to answer whether they believe that, armed with the information they had, they acted quickly enough to prevent such an ordeal for the two little girls.