My question involves police conduct in the State of: Anywhere really

How long does the average homicide/murder investigation take. I'm reading up on the CSI Effect where they say an investigation can take between 2 weeks and never. I know some cases a suspect is found and proven guilty (either by circumstance or confession) but I feel the people on other forums stating it only take 2-3 days to solve a normal case are exaggerating.

If any one could help that would be amazing!