At the begining of May 1941, Poland recruits for the Einsatzgruppen gathered in the Border Police School in Pretzsch on the Elbe River, north east of Leipzig.  The school did not have enough space to hold all the candidates, and some had to be quartered in the neighboring towns of  Duben and Bad Schmiedeberg.  Most of the candidates had come from the RSHA, whose man power division had ordered the SD and the Sipo to select suitable men for this purpose.  Another group of candidates came from the Sipo Senior officers training school in Berlin yet another group, of 100 men, had been attending an officer candidates school of the Kriminalpolizei ( criminal police ) and were dispatched from there to join the Einsatzgruppen candidates at Pretzsch.  Each of the reestablished Einsatzgruppen had sub units, usually called Einsatzkommandos or Sonderkommandos.  Einsatzkommandos were to be attached to the armed forces behind the e lines and the Sonderkommandos to those forces at the front.  However, in practice, the Einsatzgruppen and their sub units were deployed according to geographic sectors and not according to rear or front-line areas.  The distinction between the Einsazkommandos and the Sonderkommandos evaporated.  Both the Sonderkommandos and the Einsatzkommandos also had temporary sub units, usually referred to as Teilkommandos.They were sometimes called Vorkommandos when they were charged specifically with entering a town or city.