any ideas?

[Angelfishsolo]

Just a though, do you have photographs of the bike?

Also some people "not me you understand " would get a few mates together and "nick" it back. Not suggesting you do such a thing you understand but some people would do that.

 

[fossyant]

Scratches and marks are usually one of the best identifiers. Anything non standard fitted ?

 

[bmakabayan]

its really hard to say, because if the bike doesnt have any serial number, it would be very hard to prove. but if you have photo's, old photos that your son is riding that bike and the receipt of the bike, i think that will be a good proof...