The seamy details of murders were examined in the NY Times article about some recent discoveries of murdered bodies. The big news is that murderers are utilizing plastic bags more (versus steamer trunks in the old days), and that actually helps the NYPD identify the victims, not to mention figure out who might be behind the crime. Gothamist found this explanation from former chief medical examiner Dr. Michael Baden fascinating:

The plastic tends to preserve them for longer periods of time than if it had just been buried in the ground. A lot of destruction to a body comes from insects, maggots, rats and vermin, depending on where you are. The plastic is very good at preserving the tissues for longer periods of time. They can't tell the odor or they can't get to it. There are a lot of myths. In the old days they used to put bodies in lye. It turns out that lye, rather than destroy the body, preserves it, because it kills the bacteria and any insects. Plastic does the same thing.

A body found on East 13th Street last year was in a trunk.