Some past employees not getting removed from People search

We've noticed that some of our past employees still show up in People search.  Here is a comparison of two accounts:

- Employee1 - left company on 1/9/2015.  Account was marked as disabled on 1/13/2015.  His account is still showing up in People search

- Employee2 - left company on on 1/2/2015.  His account is not showing up in People search.  I'm not sure when the account got disabled.

Is there some trigger that removes a disabled account from People search?  I read somewhere that it takes three full crawls before the account will not longer show up in People search.  However, I don't think this is the case since our last full crawl was on 12/14/2014 so there have not been any full crawls since these two account got disabled.  Yet, one is showing up in People search and the other one is not.  Any ideas why?

thanks,