Remove users from SharePoint

At a client I am investigating a SharePoint farm which has been connected to another AD domain in the past and several accounts from that domain can still be found in SharePoint. For example if one adds a user to a group through a people picker, for some people two or more accounts are shown. One Olddomain\account and one Newdomain\account. (see picture)

I thought that running a Full Profile import 3 times solved the issue. But I think this will only work for accounts that are no longer in use in the Newdomain. I searched for a solution to remove the users from SharePoint and found that I can remove users from a list that can be found by typing this url: http://<portalname>/_catalogs/users/detail.aspx

After deleting the unused accounts, they no longer appear in the people picker (see below).

Tags: administration