Here is a link which lists a number of court cases which have addressed the issue of whether a police dog’s “scenting” of illegal drugs on a suspect’s currency is probable cause, with or without other factors, for arrest. (A google search for “currency drug residue” will get you a bunch of additional hits.) “Expert” testimony has been offered in these cases to the effect that 50% to 99% (variously, depending on the “expert”) of ALL US currency is contaminated with some drug residue, and that this canine evidence is therefore not worth much; but the judges in some of the cases cited have been reluctant to recognize such “expert” testimony. Is there a scientifically sound study out there which would give me accurate information on (a) the percentage of US currency contaminated with illegal drugs, and (b) explain clearly how many “parts per million” (or similar measured amount) would be required to alert a police dog to the presence of illegal drugs? Better yet, are there any studies which look at this issue based on regions or states within the US? Also, the ideal study would differentiate between types of drugs (e.g., cocaine, marijuana, etc.)
Filthy lucre, indeed! Thanks in advance for your assistance.
Ummm, money has just about every type of germ & RNA bits on it you can imagine. Money is filthy!..Cocaine? Sure, but it has aspirin on it too, not to mention just about every human body fluid there is.
I don’t know if there has been a scientific study.
William Poundstone talks about this briefly in one of the Big Secrets books. He concluded a high percentage of bills over $100 US had drug residue, but I think his percentages were still a bit lower than 50%. Maybe 10%? Drug dealers don’t deal with smaller bills, apparently. I find even these results impossible to believe, they were suggested by a defence attorney to invalidate a test used on a drug dealer and there is no reason to believe these results are that objective.
From an abstract of the Journal of Analytical Toxicology, Volume 20, Number 4, July/August 1996, pp. 213-216.
I’ve heard claims of 99%, but these are not based in fact as far as I can tell. The above study sounds methodical and credible. Law enforcement agencies and the organizations training drug sniffing canines generally downplay these kinds of studies, but it seems clear that residue on currency alone is not sufficient evidence.