From his war memoir Crusade in Europe:

The same day [April 12, 1945] I saw my first horror camp. It was near the town of Gotha. I have never felt able to describe my emotional reactions when I first came face to face with indisputable evidence of Nazi brutality and ruthless disregard of every shred of decency. Up to that time I had known about it only generally or through secondary sources. I am certain, however that I have never at any other time experienced an equal sense of shock.

I visited every nook and cranny of the camp because I felt it my duty to be in a position from then on to testify at first hand about these things in case there ever grew up at home the belief or assumption that 'the stories of Nazi brutality were just propaganda.'

Some members of the visiting party were unable to through the ordeal. I not only did so but as soon as I returned to Patton’s headquarters that evening I sent communications to both Washington and London, urging the two governments to send instantly to Germany a random group of newspaper editors and representative groups from the national legislatures. I felt that the evidence should be immediately placed before the American and British publics in a fashion that would leave no room for cynical doubt.