While they were proceeding to search every object in the inn that might possibly throw some light on the cause of death, Castaing, still at large, absented himself for nearly two hours. No one knew what he did in his second absence. He pretended he wanted fresh air, and stated that he was going for a walk in the bois de Boulogne.
M. Pelletan returned at ten o'clock next morning to make the post-mortem examination.
He had left Castaing in full possession of his liberty, but when he returned he found him under the surveillance of two policemen. Castaing appeared very uneasy at the results to which a post-mortem examination might lead; but he seemed to feel sure that if the body did not present any trace of poison, he would be set at liberty immediately.
The examination took place and an extremely circumstantial official report was drawn up; but nowhere, either in tongue, or in stomach or in intestines, could they detect the presence of any poisonous substance. As a matter of fact, acetate of morphine, like brucine and strychnine, leaves no more trace than is left by congestion of the brain or a bad seizure of apoplexy. It was because of this, a fact which Castaing knew well, that when the priest had asked him from what his friend was suffering, he had replied, "He has brain fever."
When the post-mortem was finished, without having revealed any material proof against the suspected person, M. Pelletan asked the procureur du roi if he had any objection to Castaing being informed of the result.
"No," replied the procureur du roi; "simply communicate the result to him in general terms, without making him think it is going to be either in his favour or to his detriment."
M. Pelletan found Castaing waiting for him upon the staircase.
"Well," he asked the doctor eagerly, "have you concluded and come to release me?"
"I am unaware," replied M. Pelletan, "whether they mean to release you or to detain you; but the truth is we can find no trace of violent death in the body of Auguste Ballet."
In spite of the temporary absence of material proof, Castaing was kept a prisoner. The preliminary investigation began: it lasted from the month of June to the end of September.