Expert testimony
It was Muir's intention to first establish Inspector Collins' credentials as an expert in the field of fingerprinting before the jury, then explain, in layman's terms, how fingerprinting worked as a means of identification. Collins was then made to discuss the fingerprint involved in the case. He showed the jury the cash box that was recovered from the scene, the fingerprint that he was able to obtain from the box, and demonstrated how it matched with the right thumb print of Alfred Stratton, for up to twelve points of agreement. At the request of a member of the jury Collins also demonstrated the difference in a print caused by various levels of pressure.
After Collins took the stand, the defence called Dr. John Garson to the stand. They were hoping to discredit Collins' testimony by establishing his credentials as one of Inspector Collins' mentors, thus giving portraying to the jury that he was more of an expert than Collins in the study of fingerprinting. As expected, he testified that upon examination of the print taken from the cash box and that of Alfred Stratton, he would say with certainty that they were not in agreement.
However, the defence failed to reckon the fact that Garson was not an expert of fingerprinting but of anthropometry, its rival field in identification. As a matter of fact, he spoke against fingerprinting in the Belper Committee. And there was one more thing of which they were unaware, which Muir intended to use to his advantage.
In cross-examination, Muir called into evidence two letters, each written by Garson. One letter was to the Director of Public Prosecutions, the other was to the solicitor to the defence. Each letter said that Garson would be willing to testify for either side in the trial, depending on who would pay him more.
- MR. MUIR. — How can you reconcile the writing of these two letters in the same day?
- The witness (Dr. Garson). — I am an independent witness.
The judge, Mr. Justice Channell, remarked that after writing two such letters he would opine that Dr. Garson was an "absolutely untrustworthy" witness.
Having shattered the credibility of Dr. Garson as a witness, the defence decided not to call Dr. Faulds as a witness, fearing that Prosecutor Muir would have something to discredit him as well.
