Allied leadership was very wary of running into the issue they did in WW1 - where the exaggeration of German war crimes discredited the propaganda apparatus of Britain. As they became more aware of the nature and extent of the death camps, Allied leadership opted to document evidence for the postwar tribunals rather than engage in a war of accusation and denial against Nazi Germany which could have seriously damaged the short-term credibility of their propaganda efforts.
Whether this was the right choice is another question entirely.
Allied leadership was very wary of running into the issue they did in WW1 - where the exaggeration of German war crimes discredited the propaganda apparatus of Britain. As they became more aware of the nature and extent of the death camps, Allied leadership opted to document evidence for the postwar tribunals rather than engage in a war of accusation and denial against Nazi Germany which could have seriously damaged the short-term credibility of their propaganda efforts.
Whether this was the right choice is another question entirely.