eDiscovery issue

I need to programmatically (C#) get information about all cases, their in-place holds, and sources.
Looks like classes from the  Microsoft.Office.Server.Discovery namespace are the only way to get the info I need, however I stuck with a problem - whenever I try to access the Sources_Client property of the SourceGroup class I get the InvalidCastException.

SPWeb web = ...
Case cs = new Case(web);
SourceGroup sgroup = cs.SourceGroups[0];
SourceCollection sources = sgroup.Sources_Client;

Can you please help me out with this? Is there any other way to list the cases and their detailed information?