I was on a jury last month, an assault and battery case in which the identification of the rusty-colored substance on the grip of a handgun could easily make a big difference. We convicted on the assault and acquitted on the battery because of the lack of the evidence, though I think most of us thought the defendant was guilty of both.
This was the second try at this case after a prior jury hung, but the two years between the charge and the second trial were not enough to get _any_ results back on the substance. Apparently the lead time required is such that they didn't bother to try. Here's how they explained that: "This isn't CSI."