The lead investigator Serino didn't believe Zimmerman's version.
Police did not administer a drug and alcohol test or an immediate background check on Zimmerman, although they did both on Martin.
The next day, detectives re-enacted the shooting with Zimmerman at the scene. They also discovered Zimmerman had two prior arrests: one for assaulting a cop, the other for domestic abuse.
For the next two weeks, lead investigator Chris Serino pursued a manslaughter charge against Zimmerman.
Police interviewed at least six witnesses. But none of them saw how the confrontation began or the shooting that ended it. On March 12, police gave the case to State Attorney Norm Wolfinger. He told them they needed more evidence to arrest Zimmerman.
The case now rests with special prosecutor Angela Corey, who with investigators has been quietly re-interviewing witnesses and examining evidence.
http://www.cbsnews.com/8301-201_162-57406183/video-shows-zimmerman-without-blood-bruises/

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