As to why Z was not arrested at teh time of teh incident, this FL statute may clarify it a bit.
776.032 Immunity from criminal prosecution and civil action for justifiable use of force.—(1) A person who uses force as permitted in s. 776.012, s. 776.013, or s. 776.031 is justified in using such force and is immune from criminal prosecution and civil action for the use of such force, unless the person against whom force was used is a law enforcement officer, as defined in s. 943.10(14), who was acting in the performance of his or her official duties and the officer identified himself or herself in accordance with any applicable law or the person using force knew or reasonably should have known that the person was a law enforcement officer. As used in this subsection, the term “criminal prosecution” includes arresting, detaining in custody, and charging or prosecuting the defendant.
(2) A law enforcement agency may use standard procedures for investigating the use of force as described in subsection (1), but the agency may not arrest the person for using force unless it determines that there is probable cause that the force that was used was unlawful.
So it may be proper that Z was not arrested on the spot as some insist. Innocent until proven guilty--or at least until there's sufficient evvidence warrenting an arrest.