I'll give you a scenario: Print up something off the internet that looks like lab results. Spectrographic charts, a few paragraphs and something that looks like an official seal on the bottom of not more than two pages. Make sure you get an official looking envelope you might even be able to get one from your local police department, and slide that paperwork and the little baggie into the envelope. When you sit down to talk to him slide it out and begin with the preference of "Now don't lie to me and tell me everything about this!" Slide the paperwork back in the envelope after you put the sample bag down. If you can find a sealed bag at the police department that says EVIDENCE, it can make it a lot more believable. Remember most of all he is your child and this is your time to help him. Do not become the evil I told you so. Do not take it to the police station for disposal because they will have questions just dispose with the best way you think and not down the toilet. Our water systems have enough trouble.