Thats not who it works. Again, the police do not determine these things, they can not just slap manslaughter charge on him. The state attorney is the one who does in a self defense situation. Again you and I don't know the full details, it's up the police to figure it out, present it to the state attorney, who determines whether to go for a charge.
Self defense cases are very tricky as even following procedures, to figure out whose in the right is no simple matter. Being in Florida, a grand jury panel of about 20 civilians will be deciding if the shooting was justified, and what charge will be attempted for a trial jury court case.