The police did not arrest Zimmerman because after they investigated this, THOROUGHLY, they decided that they lacked probable cause.
The police were overruled by a political racist pandering political system and Zimmerman was forced to go to trial anyway.
Perhaps Zimmerman's attorneys want to get a LEGAL RULING showing that there was NO PROBABLE CAUSE to arrest Zimmerman. The lawyers would naturally want to take this case out of the trial jurisdiction because they believe the legal personnel showed obvious bias against Zimmerman.
If they can get a legal ruling showing that there was no probable cause to arrest him, then that may remove a major impediment to filing lawsuits against the people who forced this to trial, in other words, denying them "qualified immunity," because a reasonable person with the same qualifications and experience would not have done this to Zimmerman. Just a guess, but it could be very very bad news personally for those who prosecuted him if it is ruled that there was no probable cause for arrest.
Nice guess, but probably not.
Zimmerman’s lawyers filed all documents on his web site. There is nothing there. So unlikely from his side.