What is to prevent the chemist from just cutting the coke after snorting some of it. Coke comes in 10% baking soda, goes out 15% baking soda, and who is in charge of figuring that out? The person that did it...
you realize that would help the defendant, if anything, right? perhaps even to the extent of getting the evidence excluded entirely?
(also chemists generally don't want some random guy's cocaine. they know the awful shit street drugs get cut with. once you're DEA registered, you can basically just order pure drugs from the government. that's the stuff that gets diverted, and it's also how you'd up the concentration of a defendant's sample.)
even so, that's why two people are supposed to be present for the handling, and samples should be homogenized early on and then split up for independent testing if the defendant wants it. add on lots of tamper evident tape, etc.
"and the DEA can check your records any time. they have caught at least some people (who were "diverting" cocaine up their nose) with this."
It would be trivial for any chemist to "divert" cocaine up their nose and not get caught if they put some thought into it. As you said, some already do "divert" cocaine up their nose, so obviously some chemists are interested in random guy's cocaine. If the DEA is catching people through record keeping, you can be sure there are some chemists who sensibly doctor the records at the same time.
If the chemist is interested in doctoring lab results to screw over a defendant (rather than get high).... well shit, we already know that is possible, don't we? That is the entire point of this discussion. There is really absolutely no sense in arguing that chemists cannot doctor evidence to send some guy up the river, we already know that they can.
