Criminal organizations don't have written constitutions that say “this criminal organization is a money-laundering shop”, so we tend to have to rely on hundreds of hours of wiretaps. Members of organized crime groups know they're being wiretapped, so you have to play a lot of them. You often have to rely on insider witnesses--agents or turncoats. Their testimony often will take days and weeks. They'll be cross-examined at length because they tend to have unsavoury backgrounds.
Just to meet the definition requires a lot of evidence. That's the difficulty. We have to prove it beyond a reasonable doubt. As well, a lot of these groups will also have facades. They will try to do legitimate activities, such as toy runs and that sort of thing. They'll say that they're just a bunch of guys who hang out in a house, drink beer, and play cards.
You have to go beyond that. That's the difficulty. It's the covert evidence that takes a long time to get out.