At his address they discovered more than 5,900 scans of passports, identity cards, utility bills and bank statements relating to people from countries including the US, Canada, Australia and New Zealand.
It does rather look like he got hold of a casino's verification database. It's not just passports, but for each ID he seems to have the set that players have to send to a casino on their first withdrawal.
I expect he is merely an end user, having bought these files from a criminal network.
It is also possible that the network obtained these documents by opening a "front", a fake casino like, for example, Ministering Angel, and asked players to send in their documents after they requested their first withdrawal. They could have run the scam for as long as they could circulate the money among the players, and then simply done a runner once they had enough documents to sell on.
I am surprised the UK Gambling Commission and the police's own gambling unit didn't pursue this worrying question of "where did 5900 sets of player details come from", because as players we KNOW that the current verification systems are riddled with enough security weaknesses that it is only a matter of time before a very large database, and a COMPLETE one, gets stolen from a casino and then sold on to the criminal "fraud rings".
He was not convicted of "bonus abuse", but of FRAUD. Mere "bonus abuse" is a civil contract matter that would never go in front of a criminal court, and in this industry, rarely goes before a civil court either.