Lots of "policework" and forensics investigation has been shown to be so incredibly fallible that its scary that we rely on it so much. Even the scientific analysis itself is an issue (its often highly subjective), and that's before you get to a lot of outright bullshit (where "experts" literally had just paid a diploma mill for a degree and had no actual credentials). Frontline I think has had several good episodes about some of this. There was one about how arson investigation was often completely wrong. Dog sniffing has been shown to be very unreliable, I think blood splatter analysis was shown to have serious flaws, and then stuff like DNA, fingerprint, and hair analysis has serious issues.
Ideally that's why you try and find as much evidence as possible to build as many indicators as you can, but I think some study has shown that bias runs throughout and can railroad cases where the evidence is actually lacking when held up to scrutiny.
Its why I have mixed feelings about how technology is going to enable basically constant surveillance. On the one hand, lots of scary implications, on the other, most crimes should have tons of evidence to show what happened. I think the important thing is that the technology be available to everyone, that way we have watchers watching the watchers watching the watchmen. Until robots enslave everyone.
Oh, but about sketches, wasn't there some movement to have the police kinda open source this, where they'd release witness descriptions and artists could sketch them and see how they match and then tweak them to see if they could get them more right? Maybe that's just high profile cases or something, but I recall there was some talk about doing that, and it would in theory improve that process.
Last bit, there's also possibilities that they got the wrong guy, or there were multiple ones operating. That was another major problem (and continues to be) is that police departments would often deliberately not share information, and so criminals could drift or hop back and forth and it take them a long time to actually link the crimes. And in some cases (Adam Walsh for instance) there were multiple serial killers that could potentially have been in that area (wasn't Dahmer down there? Bundy was, and then Ottis Toole and then the whole mess with Henry Lee Lucas). There seems to be a lot of potential crossover for who is doing the killing in a lot of serial cases. On the Science channel I remember some show being advertised and it allegedly used scientific analysis to look into more disappearances and things, and the ad had "there seem to be a lot more serial killers operating than we thought/think" and that there could be a lot more cases that just never really make the news. Although often quite a bit of that has shown to be very sketchy (for instance there's some bigfoot hunter person that claims that there's been thousands of people go missing in national park, and bunch of weird "evidence" in the ones they do find, but the end result is that it basically took some weirdness in that the national parks department apparently didn't/doesn't keep a database of people that go missing in the parks, and blew it into some big weird conspiracy thing and then used it being not taken seriously by authorities as evidence of the conspiracy) so not sure if there was much real validity to it (never saw the show).
Actually right now I'm watching a documentary on Netflix about Johnny Gosch, and look up that situation and see how crazy of theories and things it leads to (you'll end up at pizzagate eventually by the way, as there's a long running belief about sinister pedophile rings that go to the highest levels of government/society, with basically every President for I don't know how long being involved).
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