Hollywood has never been afraid to sacrifice realism for the sake of an entertaining story. And since pretty much every movie or TV show features the police in some way, we as an audience get fed a lot of total horseshit about how the law works and how cops operate in the USA.
But as most of us are on the outside of the judicial system (for the moment) we usually don't even realize that what we're being told is incorrect. So we just accept things like...
7Forensic Science is Magic
As Seen On:
The various CSI shows, Bones
There has been a murder. While the regular cops are all wasting time talking about "witnesses," "motives" and "evidence," the CSI team walks in and gets shit done. Within seconds they find a single hair, scan it with a green laser and discover the identity of the killer, saving countless lives with their ingenious magical science. Hell, the CSI team will even pack up their guns and go arrest the guy!
His one mistake was having hair.
Why it's Bullshit:
First, do you have any idea how much random DNA you are carrying on the soles of your shoes this very instant? A hair from that bank clerk across town, gum from a Pakistani cab driver and semen from an undetermined source are all probably crawling around down there, ready to be tracked through a crime scene.
Also, certain laboratory tests such as DNA samples, toxicology and blood reports can take weeks or even months to process, and when they do finally arrive, they are about as clear cut as the plot to The Phantom Menace.
"Wait, they're racing now?"
Also, while DNA criminal databases do exist, less than 1/10th of all criminals are a part of it. Having a bit of DNA doesn't mean shit unless they have something to compare it to.
That means the CSI stuff is less about finding the killer and more about making sure they have enough evidence to convict the guy they've already pinpointed as a suspect through old-fashioned police work.
CSI is really just another victim of bad Hollywood science, kind of an extension of their "computers are magic" philosophy. It's appealing to think that any problem--even crime--can be stopped cold by nothing but the power of science and human intellect. Add a few dead hookers and an exploding car to the mix and you have the recipe for television success, baby.