I assume you have two tables, one is Inmate information and the second table has details about the inmate. Something on the order of Customers and Orders where One Customer can have Many orders. In your case it would be One Inmate and Many 'somethings' (I don't know what it coud be). Here is how your tables might look:
tblInmateInformation
InmateID (Primary Key and Autonumber)
LastName
FirstName
MiddleInitial
...other fields
tblInmateDetails
DetailsID (Primary Key and Autonumber)
InmateID (Foreign Key and Long Integer)
...Whatever fields you need
The above would be an instance where you would have a Main Form (InmateInformation) and a Subform (InmateDetails)
If this is the setup you have then your tables will be joined on InmateID (in the relationships window) and in your main form the combo box will be based on the InmateID, LastName and FirstName. Therefore the Master Link in your Subform would be the Combo box and the Child Link would be the InmateID.
I hope this makes sense to you. If you do not have a setup like this then a subform is probably not appropriate for what you want to do.
hth,
Jack