Crystal Reports fields with similar values

Message

hello, i have 2 fields im trying to add to a report.   
The first is officer, the second is investigator.  These fields are numbers in the database.  For instance officer 1 is smith and officer 2 is jones. 

I need a formula that I can assign  the investigator field to point back to the employee table and pull the officers last name instead of the number.  

I made the formula {emmain.emlname} &","& {emmain.emfname} for a generic one, but I don't know how to assign the field so that 
officer = {emmain.emlname} &","& {emmain.emfname} or 
investigator = {emmain.emlname} &","& {emmain.emfname}

any suggestions on how i can assign those values to each individual field?

Thank you!