From article:
Police saw white dust on the floorboards of Cashe's car and tested it with a field kit. The substance showed positive for cocaine. Cashe went to jail for 90 days – 90 days in which he knew that the white substance in his car was simply drywall dust.
"Some tests ... use a single tube of a chemical called cobalt thiocyanate, which turns blue when it is exposed to cocaine. But cobalt thiocyanate also turns blue when it is exposed to more than 80 other compounds,
http://www.npr.org/sections/thetwo-way/2017/10/16/558147669/florida-man-awarded-37-500-after-cops-mistake-glazed-doughnut-crumbs-for-meth
Say what? I mean turning blue for 8 compounds other than cocaine would be bad enough ---but 80!