not my forte but you can use variable formulas based on group summary data. These assume you are doing a count of 'offender' per 'officer' group. These also need to be displayed in the report footer.
//highest number
numbervar highestvalue;
highestvalue := if highestvalue > Count ({table.offender}, {table.officer}) then highestvalue else Count ({table.offender}, {table.officer})
//lowest number
numbervar lowestvalue;
lowestvalue:= if lowestvalue <>0 and lowestvalue< Count ({table.offender}, {table.officer}) then lowestvalue else Count ({table.offender}, {table.officer})