While the activities of the Police Regiment South, the Einsatzgruppen detachment and the 1st SS Brigade, progressed, the reports by the murder squads were being intercepted and decoded by MI6, the British intelligence service. As part of Ultra, British signals intelligence program, the codebreaking facilities at Bletchley Park decoded and analysed the messages. The head of MI6, Stewart Menzies, communicated the decrypts directly to the British Prime Minister Winston Churchill.