It sounds to me that Bitcoin is a lousy medium for money laundering. It's unclear to me whether they laundered money by supposedly buying and selling bitcoins or converted shadowy assets into BTC and then back to physical currency, but in both cases the transactions can be tracked back in the blockchain so you'll not only have to make a good story of where the money came from but also, if and when the authorities get interested, make sure that how the BTC is moved around reflects that story.

But merely converting BTC to cash via ATMs doesn't even sound like laundering to me at all, just conversion. You would still need to explain the cash you've acquired if you intend to buy something with it.

Money laundering itself is not for those in a hurry. To plausibly launder money you need a service business with costs that are rather fixed and customers who can plausibly pay with cash. Then you can have as many "customers" as you like and nobody can really tell how many you really might have had but depending on how you set up the scheme you can report a reasonable income over the months and years, pay the taxes and thus turn the money legally earned.