Resolution of crimes is a toss up between doing the best you can forensics, and being aware of the rules for evidence, with an eye on an annual budget for service .Many of these crimes require expenditure of heavy funds in order to compile piles of indesputable forensic evidence which , even after its all done and agreed to for admissability, is still circumstantial.
I recall one case where my team was hired in forensic geology and botany. e were asked to locate and date a buried tool used in a murder.(It was a van that was buried and lay that way for about 15 years)
e located it using geophysics, then the police agency hired a forensic anthropologist and assigned criminologists to learn everything about the the truck and its association w the crime and murders under investigation. We were then re assigned to have our biologist work with a university botanist to determine what time in the year was the vehicle buried (from pollen analyses). Later we gathered up county wide planning aerial photos that were flown every 3 years. The site, after mapping and surveying was covered in sequential air-photos for about 15 years so we had several overlapping routes of evidence that this was, indeed, the site where a crime tool was disposed.
After all this was done all the circumstantial evidence was tossed out because the cops arrived at selecting the candidate burial sites by unconstitutional means. The guys walked, and one of em was shot down in subsequent crimes in which he took part, the second guy was arrested on another major crime and confessed and was sent to do time as a "career criminal" under Pa's early version of "three strikes" and the third guy seemed to have disappeared from view forever.
At the time, the case involved about 2 million dollars of investigation and case prep, (witnesses, evidence, chains of custody etc). This was in the 80's, DNA was not mature and was only being proposed in a few cases due to the prevailing Frey decision about scientific evidence. Daubert and Rule 702 largely superseded Frye but that wasnt till the mid 90's .