He also said he did not pull the trigger. Here is the problem. Since about 1915 most revolvers have a hammer block which prevents a revolver from firing without squeezing the trigger. Simply pulling the hammer back will not allow it to fire.
Old Fashion revolvers will fire because they don't a hammer block. BUT, in order to make if fire you have to pull the hammer back and release it. That is why back in the day many carried the weapon with the chamber that was under the hammer empty.
So I want to know did the gun have a Hamer Block or not. If it did, he pulled the trigger. If it didn't, he dropped the hammer.