"There are only two possible reasons for a police department to be using a test like that [with a known 70% false positive rate]. The first is ignorance, but of a degree and nature that is quite scandalous. The second is to commit fraud upon the courts, by claiming to have evidence of drug possession where no drugs exist. In light of the FBI hair test scandal (https://www.washingtonpost.com/local/crime/fbi-overstated-fo...) I think the latter explanation is fairly likely."