“the chief of police went to the station personally for Zimmerman on a Sunday night”
Maybe the Chief of Police showed up to work because he had a homicide case to deal with. Wow. What information is there that because the case involved Zimmerman he decided to go to the station? On a Sunday night means nothing special. You show up to work when duty calls. Why would the Chief not consult with the state attorney?
And everyone with half a brain knows that in a potentially controversial case most officials understand it's best to take the cowardly way out (an arrest). Which suggests that they knew they would end up with an expensive prosecution that amounted to nothing, and thought the evidence was already so strong on the side of self defense they didn't have to take the cowardly way out.