The following letter from General H. R. Alexander to commanders and men of the German army is from the British National Archives.
Unfortunately, it is undated. However, as the last of the atrocities listed in it allegedly occurred on October 2, 1944, it is apparent the letter was written sometime after that date and before the end of the war in Europe.
My access to the document is courtesy of British researcher Brian Sims.
Here is the full text of the letter:
WARNING to German officers and men
By General Sir H. R. Alexander, Commander-in-Chief, Allied Armies in Italy.
1. Reports of atrocities – killings of hostages, mass reprisals against innocent civilians, torturings and the like – committed by German troops in Northern Italy are becoming daily more frequent.
2. I therefore call the attention to all German officers and men in Northern Italy, who otherwise might give or carry out orders to commit such atrocities, to the following:
3. The fact that in, for example, a certain village Italian patriots – whether or not wearing uniforms, arm-bands or other recognizable insignia – may have attacked German soldiers is not, according to the Jus Gentium or any other Legal or moral code, a justification for collective reprisals upon the population of the village, nor for the killing or persons without due legal trial and conviction.