Theft of articles of art is often ordered by private collectors. Such collectors get an incredibly valuable item for under $100K. The item then, entirely invisible to the taxing authorities, remains in the family. Decades later it sails past the death tax and becomes inherited. Even later, once the trail is cold, the item may be sold at an auction. Note that such a violin is above any fiat currency because Antonio ain't making more of them. As a store of value they are better than gold and diamonds because you can always mine more of those.
That is getting harder and harder to do, because of modern forensics and modern technology.
You would have to keep the Strad in the family (under omerta) for 200 years before getting away with a caper like this.
This may have been the thought behind the family of Israel Swift, that owned about 10 of the 1933 Double Eagle, a coin that was never put into circulation and thus never was official. The most famous of these was a single example that wound up in the collection of King Farouk of Egypt, with a 'legitimate' export license and thus 'official'! It ended back in the US at a 2002 auction for a bid of $6.6 million and total price of $7,590,020 with the last $20 going to the Mint for official 'monetization'.
In 2005, the US seized 10 more of these coins, in a safe deposit box, from the same dealer (family) Israel Swift, who sold the original that ended up in the above auction. In 2011 a jury trial gave the verdict that the coins were stolen property and belonged to the US Government. The family is still appealing the $50+ million loss!