I tell people CSI is science fiction. Many things they do may be theoretically possible but aren't a reality, yet. DNA evidence for instance can not be processed in less than 36 hours. Local police departments generally don't have this capability and the labs that do have a back log that is sometimes over a year long.

Oh, and NCIS specifically doesn't have a crime lab. They send their evidence to the Army's lab in Atlanta. Hopefully you hear back something before you change duty stations!

Real investigations are solved largely though interviews and interrogations using much more mundane evidence. Criminals, by in large, are incredible dumba---es and tend to let their mouth do them in.