Although Sheila Birling has already said that she thinks Inspector Goole may not really be a policeman, it is Gerald who first makes enquiries to ascertain the truth of this. When he returns to the Birlings' house in Act III, his attitude to the entire incident has become thoroughly skeptical. His principal question, which has not yet occurred to the Birlings, is how they are to know the girl with whom they became involved is the same girl in each case. He points out that the Inspector showed both Mr. Birling and Sheila a photograph, but they have no way of knowing that it was the same photograph. He then adds:

We've no proof it was the same photograph and therefore no proof it was the same girl. Now take me. I never saw a photograph, remember. He caught me out by suddenly announcing that this girl changed her name to Daisy Renton, I gave myself away at once because I'd known a Daisy Renton.

Gerald's growing certainty is fueled not so much by positive evidence as by the lack of any evidence to the girl's identity. His case is clinched, however, when he telephones the local infirmary and asks whether they have had a suicide of the type described by the Inspector. They tell him that they have not had any type of suicide for months, and it becomes clear that the Inspector's story must have been a fabrication. The girl who died from drinking disinfectant therefore does not exist, and the Inspector's care in never showing his photographs to more than one person at a time strongly suggests that Eva Smith and Daisy Renton are two or more different people.