Fraud or not.
It is rare for casinos to come clean about fraud. Many players tied up with the BelleRock case were simply being told to forward documents. This, in many cases, turned out to be a delaying tactic to give them time to investigate, as players who forwarded documents were then given other reasons for the delay, including the casino then asking for Notarised documents, something that is very unusual, and is a dead giveaway to a player that their account is flagged for possible fraud.
Any time a player is told their account is "under investigation" AND it has been locked, it is 99%+ that they are under investigation for some kind of SERIOUS breach; beyond what the casino considers a minor matter that can be dealt with by the usual means of simply telling the player what they need to do, such as wager x more to meet WR.
Recent cases seem to suggest that the casinos resort to mass account lockings and refusal to pay. One hope may be that the fraudsters will simply give up after receiving their deposit back and have a go elsewhere. Innocent players who do NOT fight hard are believed to have gone away because they are guilty, so it is essential to complain hard, and quickly, but stick to the facts and proper order at first.
Once all legitimate channels have run their course, then it is time to get really aggressive, since at that point the player has little to lose. Most complaints get sorted before this stage, but some players have found that after becoming more aggressive with the complaint the casino somehow "finds" the mistake they made and pays up.
This happens in business in general, with businesses only really listening at a high enough management level when complainants get aggressive to the point of causing the business bad publicity. Many times, the mistake is really stupid, and the business is made to look a right t*** when they have to publically admit that it was their mistake all along. Local authorities are the worst offenders, followed by the big utility companies with their natural partial monopolies. Casinos get away with it, despoite the lack of a monopoly, because they already have your money, leaving you, the customer, far less room to manouvre than in the case of a really stupid cock-up with a bill yet to be paid (they say "pay up" or go to court - I say go-on, take me to court and look a right D*** head in front of the judge).