There are lots of situations where some information is not known to the county attorney immediately after the arrest. One example is the Blood Alcohol Content in a DWI case (when the police took blood instead of a breathalyzer). The blood can take months to analyze (because the forensics lab is overwhelmed). This matters because the BAC level determines which level of offense the county attorney must allege. There are also times where the type of drug needs to be determined by a lab or prior criminal charges from out-of-state convictions need to be confirmed.