Eyewitness identification and testimony - Is it reliable?

"Believe none of what you hear and half of what you see." - Benjamin Franklin 

The uproar surrounding the alleged shoving of Rep. Reecy Dickson (D - Macon) by a reported Tea Party member has been the talk of the Mississippi political world today.  Some folks say Rep. Dickson was shoved, some say she was grabbed, some say she wasn't touched at all.  Regardless of what happened, the State Capitol Police investigated and no charges were pressed.

But that leaves a lingering question, doesn't it?  How can so many supposed eyewitnesses claim so many versions of the event as the truth?