Berlin police are trying to find out who opened the unmarked grave of SS officer Reinhard Heydrich, a top Nazi killed by Czechoslovak agents in 1942. An employee at the Invalids' Cemetery in central Berlin found on Thursday that the grave had been opened. No bones were removed, police say. Heydrich was a key organiser of Nazi Germany's mass murder of European Jews. He chaired the Wannsee Conference in January 1942, where Hitler's genocidal "Final Solution" was planned. Tampering with a grave can be prosecuted under a German law against "grave defilement".