High Traffic Murder

This is going to be a more gloomy type of post.  I have been listening to little snippets of the 'Tragedy in Tuscon" and it made me think....what if someone was murdered in a high traffic area with nobody else around?  How would they be able to find who the murderer was?  For instance, say someone was in Wal-Mart or some other big retail company and, for some odd reason, nobody else was around.  Maybe the store was already closed...who knows.  The murderer knew what they were doing and killed cleanly and meticulously...but they forgot about one thing...to wear gloves.  Now, think about how many people are at a big retail store each day...500 or more right?  They're touching everything and checking different products out so there are fingerprints all over the place.  So, when the investigators come in to gather evidence, how will they know which fingerprints are which?  Do some fade with time?  Can they tell how long the fingerprints have been there?  It's just some random question that popped into my head yesterday.