But what if the experts are divided on what the black and white stuff says?
One spring morning in London in 1905, William Jones discovered the door of the Oil and Colour shop where he worked unexpectedly locked. When the door was broken down the body of the proprietor, Thomas Farrow, aged 71, and the mortally wounded body of his wife, Ann, aged 65, were found, as were two cast-off black stockings which had presumably been used as masks.
There was strong circumstantial evidence for believing that the brothers Alfred Edward and Albert Ernest Stratton were guilty of the murders, but there was nothing nearing absolute proof until a fingerprint was found on the forced-open cash box.
The leader of the investigation, Detective Inspector Charles Stockley Collins, the foremost fingerprint expert in England, was certain that the fingerprint (which turned out actually to be a thumbprint) belonged to Alfred Stratton; but would a jury accept this very new kind of evidence as something strong enough to hang a man? Testifying for the defence was Dr George Garson, who was believed by the defence team to be a very great expert in fingerprints. (He was actually nothing of the sort: he was a fervent advocate of anthropometry and saw the modern trend for fingerprinting as a poor rival to his own speciality.)
Dr Garson gave evidence that he could not with certainty identify the print on the cash box as having been made by Alfred Stratton - but during the cross-examination two letters of Dr Garson's came to light.
One was to the solicitor for the defence, and one was to the Director of Public Prosecutions, who organised the prosecution. The letters had been written on the same day, and in both Dr Garson expressed himself willing to testify for either side, depending upon which side would pay him more money.
Dr Garson was hence proved to be, in the judge's words, 'an absolutely untrustworthy witness' and the defence case collapsed.
The Stanton brothers were found guilty of the two murders.
They were executed on 23rd May 1905.
Word To Use Today: proof. This word comes from the Old French preuve, a test, from the Latin probāre, to test.
Unless you're a Scottish lawyer, the past tense of to prove is conventionally proved, not proven.