Most murders aren't the TV episode kind. They're the gang-related, drive-by, ass-capping kind.
Still, if you wanted to off somebody and get away with it, all you have to do is not be stupid. The burden of proof is so high that there has to be a believable witness or clear, undeniable, direct evidence against you or you won't even be charged. Either that, or they need a confession.
That's why most police detectives are, essentially, interrogation specialists. And by the term specialist, I mean a fat guy who denies you food, water, sleep, or bathroom privileges and screams at you at the top of his lungs for 24 hours.