Who is behind Karachi Killings?

About the recent Karachi killings, the Interior Minister, Rehman Malik says that a 'Third' force is behind these killings and that the ANP and MQM are not to be blamed. Every one knows that there are three main forces in Karachi. 1. MQM, 2. ANP, 3. PPP. Is the 'Third' force PPP, which the interior minister is referring to?