And the top-rated comment there, by jimrandomh, is still the first and last word on the matter as far as I'm concerned, even in light of the WashPo's editorializing:
"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."
The key words there are "police department." I agree 100% that a police department should be held accountable for using a test that appears to be about as useful as a Cracker Jack decoder ring. But this case was about the officers' personal liability. As the article points out, the legal question here was "Could a reasonable officer believe he had probable cause?" Whoever chose this particular test should be held liable—not the people who got it off the shelf and followed the directions on the box.
But I would note that the plaintiffs are suing the "Board of Commissioners of the County of Johnson County, Kansas et al." [1], not officers Joe Blow and Bob Smith.
Agreed. I think it can be fairly argued that the officers in question did not, in fact, know how shitty their field test was. Unfortunately it could just as fairly be argued that they did know and would gleefully make use of an investigative tool they knew was faulty at every opportunity just because it increases their odds of making an arrest (and then lie about it).
As far as ignorance goes, check out this fascinating quote from the judge:
"In fact, as plaintiffs point out in their submissions, Deputy Burns testified that, at the time he tested the plant material he discovered in plaintiffs’ trash, he had no knowledge that anything other than marijuana could test positive on a marijuana field test kit and that he was “not aware” of the possible occurrence of false positive test results. Deputy Blake’s testimony on those issues is substantially the same. Moreover, Sheriff Denning testified that, since he came to the Johnson County Sheriff’s Office in 1978, the Office has conducted “thousands” of field tests and the only false positive results of which he is aware are the results at issue in this case."
Apparently the judge is under the impression that this justifies his ruling, rather than damns both him and the entire police department.
"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."
https://news.ycombinator.com/item?id=10804016