Evidence is very powerful if used correctly, but in order to be used correctly you have to understand judicial processes and the nature of evidence. One of the first principles you come to learn is that every contact leaves a trace.
Theoretically, even a touch from a cloth glove lives an imprint in dust that is invisible but existent, a swipe from a defensive hand leaves trace amounts of DNA lodged under fingernails, a hair follicle leaves trace DNA (even though, recently, hair examination with comparison microscopy was ruled as unreliable, DNA is still reliable), cleaning with bleach leaves trace residue detectable with chemicals, a partial fingerprint leaves several minutiae points that can be used to build a case that illicites search warrants. Every bit of it, is trace evidence that puts a person in a location that is nearly infallible. Locard’s principle states that EVERY CONTACT LEAVES A TRACE, and that you just need to find it.
In court, evidence is circumstantial, meaning it’s usefulness is based entirely on whether or not its relevant, and if it’s used and positioned correctly. An unreliable witness testimony is just that, an unreliable witness testimony. Another important note would be judge or jury?And what jury, who comprises the jury; and what judge, who is the judge? Lawyers assign favorability, after an interview called voir dire, then choose them based on relevant life experiences, physical similarities like age, race, maybe even things like height if the lawyer is playing some psychological gamble game and senses resentment for being a specific height, or whatever, in any case is relevant. The jury has the facts read out to them, with an expert witness (with relevant vocational and educational experience) usually presenting evidence. Then the case has to be made for the relevency of the evidence, the value (if it puts someone somewhere, if it removes someone from being suspected (called exculpatory evidence)(e.g. DNA blood typing being done on scene finding A+ blood then doing a panel and finding the main suspect to have O- blood), if the evidence is direct in placing them there (video) or indirect (hair found in the back of a car), how rigorous or strong evidence is (certain DNA tests place people in 1/23b, making it statistically impossible (but not technically improbable) for it to be a certain person).
Given the use of evidence, and given the properties of evidence, you must understand the situationality of evidence as well. In the aforementioned examples, all of the evidence is dependent on the situation. There’s examples of chemical evidence, hidden to plain sight. There’s examples of physical evidence, hidden to plain sight. You can always find forms of evidence, you just have to look hard enough. Theoretically, one day we will be able to test for the smallest changes in chemical composition in the environment and tell who has been where, using multiple sources. Whether it be a specific mix of hormones that float in the air for a few hours, skin particles we can link to people, any minute amount of chemical residue, will be able to be analyzed and narrowed to a single person, in theory.