You are correct, it happened at Dachau, which I think was the first camp inside Germany to be discovered. The American GI’s had just found a train of boxcars in which were thousands of dead bodies. They had been delivered to Dachau but in their haste to bug out the Germans never opened the doors so all the victims had died never having a chance to get outside. It so infuriated the already stressed out American soldiers that they did exactly what you described - street justice. The goody goody REMFS wanted to court martial everyone involved but Patton refused to sign off on it and no one was ever tried nor disciplined.
Read all about it in The Liberators by Alex Keyshaw. If the tales of this unit’s trials in Italy aren’t enough to horrify you, follow it up with a The Day of Battle by Rick Atkinson. No wonder they finally snapped after a full year of fighting.
Oops...Alex Kershaw