>>>Since these are registered guns...
1. Send out a letter such as the one in the OP.
2. If the gun owner doesn’t comply after a short time (say, a month), contact him again and explain that if he doesn’t comply, he will be in violation of the law.
3. Shortly thereafter, show up at his doorstep (with a SWAT team as backup) and order him to turn over his property.
4. If he resists, kill him.<<<
In NYC, I think they would start with #4 and work their way back.
What would be the response to a sad story about that "unfortunate boating accident last summer?"
The (former) gun-owner has committed no crime - he has merely "lost" his (until then legal) firearms (and how can you be expected to "prove" that something has been lost?).
Could a judge legally issue a search warrant, even though no crime has been committed?
Regards,