It would be unusual to say the least for the case not to be solved at some stage and it could very well take someone with information to come forward. Which in itself poses the other question as to why a reward has not been offered for such information. The old excuse that it might harm the investigation just doesn't cut the mustard anymore imo.
There was a huge reward at the beginning- no takers.
There are a few reasons for this and I am quoting a senior police detective friend. of which I agree.
1. Abduction theory 1 : paedophiles would never snitch especially if there was a violent death with sexual content and this was filmed and distributed.
2. stolen by gypsies- they do tend to stick by one another however there are different types of gypsies groups/families. They are not all thieves,child snatchers- they would probably hand the child back for the reward money at the time.
3. only one or two people know what happened and they are very faithful in a pact of sorts.
4.predators known to the child had to get rid of her in case she spoke up about something untoward.
He mentions a few other scenarios.