But in reality, that isn't always the case. It's not necessarily because the science itself is wrong, but often because the humans that carry out and/or oversee the science are mistake-prone or negligent.
A recent article in the ABA Journal highlighted several cases of crime labs and similar testing facilities which produced test results that ranged from highly suspect to wholly inaccurate to intentionally fraudulent. Some of the cases cited include:the mishandling of DNA evidence in New York City over a ten-year periodthe indictment of a former Boston chemist amid allegations of faking results and contaminating drug samplesthe closure of an evidence processing facility in St. Paul, Minnesota after determining that it didn't have any operating procedures or scientific oversightthe falsification of dozens of DNA tests by a serologist working for the state of West Virginiaa chemist at the Oklahoma City crime lab who was found to have given false or misleading testimony in almost two dozen death penalty cases
No crime lab facilities in the state of Washington were mentioned in this article. They haven't been in the media since thousands of breath tests were suppressed for a three year span from 2007-2010. But the point is that just because you are presented with "scientific evidence" that a crime has been committed does not necessarily mean that the case in open and shut.