When Redditer u/Ladybugsrule asked whether "'CSI' created a false sense that all crime scenes have clear physical evidence of who committed the crime," many fans replied yes. Notably, u/buffyfan12 listed several things jurors now expect to see because of crime procedurals, such as high technology, lots of blood spatter, and lightning-fast, highly reliable DNA results. Judges and lawyers have had similar complaints about the show and jurors' expectations — especially regarding DNA testing.
DNA testing is much more complicated than it appears on television. For one, it takes weeks or months, not minutes, to get a result. And with potentially several DNA contributions to a piece of evidence, it can be nearly impossible to narrow them down. "We never use the word 'match,'" NYPD hair and fiber analyst Lisa Faber told The New Yorker. "The terminology is very important. On TV, they always like to say words like 'match,' but we say 'similar,' or 'could have come from' or 'is associated with.'" Oregon DNA supervisor Michael Koch agrees, telling KVAL, "I've seen the most surprise in jurors when we get a mixture off a piece of evidence and we can't make a conclusion."
According to Massachusetts forensic science undersecretary John Grossman, shows like "CSI" have made it "much harder" for those in his field to do their jobs. "Juries now expect high-level science to be done on lots of cases where again we don't have the resources to do them, and in many cases, the science doesn't exist to do them," he told NPR. And that ignores situations where there is no DNA evidence to be found, no matter how thorough the investigation.
