Police procedurals, whodunnits, and courtroom dramas are a big part of our entertainment, but that doesn't mean they are all that accurate. Crime fiction uses all sorts of shortcuts and tropes that just aren't so in real life, but they will keep using them as long as they create conflict and move the plot along -and ensure that the "good guys" win.
See 14 of these myths busted in a pictofacts list at Cracked.