How can we set up Person Search to distinguish between 2 Groups

We are on CRM 9.2 and have been live since summer 2014.  We have primary users or agents that work cases for our employee base at our institution.  We have one business unit and these agents can search for any employee or person of interst in system.  Now we have a 2nd group of users who want to use CRM for similar cae management, but there are some differences in who they can search or access in system.  The second group of users or agents should be able to search/access all employees, same as first group.  But the second group