[jsmith45]

From a quick machine translation, the documents basically say that NFTs (as crypto) are high risk transactions often associated with criminal enterprises, and untraceable money flows.

They think instead of being legit art sales, the NFT sales where part of a complex scheme through which he was laundering money. (Likely this scheme amounts to selling the art to himself. It is not especially difficult to have your various criminal wallets buy NFTs from yourself, making it look like legit purchases. Alternatively he and a ring of criminal associates could be buying nfts from each other with their dirty funds.)

The documents provide basically no indication of them having any evidence of this beyond "large amounts of money" moved via crypto. The documents even make it sound like that is their only evidence. But the documents claim that because they have reasonable suspicion that the money came from crimes, they can seize it.

The documents make it sound like money laundering is technically only illegal if the original source of the money is illegal, but make no effort to establish that the pre-laundered funds are criminal, and point out that the law does not require them to identify the crime from which the funds were originally obtained.

The assertion in the arrest documents seems to be basically that making a lot of money by selling NFTs is in itself sufficient cause to believe that money laundering of illegal funds was occurring, which provides sufficient justification for seizing the funds.