Most folks have a different idea of what forensic labs do in the testing of evidence. We think of lab coats and complex scientific tests like we see on CSI. It is not always true. if your arrested for possession for marijuana in Tennessee ,  the evidence seized may  eventually be tested by one of the Tennessee Bureau of Investigation (TBI)  crime labs. How do they test marijuana for use in the court room ?

First , marijuana is examined under a microscope to determine botanical identifications  The lab person is looking for trichomes . Some organizations suggest there must be training in botanical identifications in order to make these findings. The data should also be reviewable in evaluating test reports. For example , a picture taken of the examination. Easily done with a digital microscope , but not done by the TBI .

The next test is the use of the Duquenois/Levine test. It is simply a reagent that is put on the marijuana and then chloroform is added. It is then supposed to turn purple. Again ., no photo is taken. That is the end of the testing that the TBI does. Is there more to the story ?

The National Academy of Science in their book  "Strengthening Forensic Science in the United States"  recommends those two tests in addition to a thin layer chromatography test. Guess what ? The TBI does not use that test to my knowledge . The Scientific Working Group for the Analysis of Seized Drugs recommends another layer of tests to confirm if a substance is marijuana. The chair of the core committee happens to work for the Drug Enforcement Administration .

The question is why does the testing for marijuana in Tennessee does not comply with the minimum standards set by two scientific groups ? Indifference. No concern of scientific accuracy. You fill in the correct answer.