[Tailback]

I get your point. Then you trace the credit card purchases at each store that recieved a shipment of that batch of powder.

[null and void]

Yep. And if he blends powders, or there is residue from several batches previously used, they only need the names of people who bought inventory from ALL of the identified batches.

That can narrow it down pretty quickly.

Of course that doesn’t mean that won’t harass anyone who bought ANY of the batches in question....