Science and the Criminal

by C. Ainsworth Mitchell

A chemical examination, however, which was made in the presence of the magistrate and the prisoner, proved that they consisted of citrate of iron, and had been produced by cutting a lemon and neglecting to wipe the blade after use.

It has frequently happened in the past that the opinion of policemen or witnesses without any special knowledge of the subject has been taken in criminal cases on the point whether stains upon clothes or on a weapon consisted or did not consist of blood.

This practice was obviously a dangerous one, since even by the modern methods of examination it is not always a simple matter to be sure of the fact.

Until a comparatively recent date the tests for blood-stains were based upon bringing the colouring matter of the blood into solution and applying chemical tests to establish its identity.

The necessity for scientific proof of the presence of blood-stains is shown by numerous cases in which stains of similar colour have at first been attributed to blood.

Thus in a case related in Taylor’s Forensic Medicine a man was arrested in 1840 on suspicion of being connected with a murder in Islington. He had in his possession a sack on which were numerous stains supposed to be dried and coagulated blood. When these were examined, however, they were found to be due to red paint.

In another case, a man who was suspected of a murder was found to have red stains on his shirt and collar, but as these would not dissolve in water they could not have been due to blood. Subsequently it was found that they had been caused by the man going out in the wet with a red handkerchief round his neck.

An early example of the way in which the evidence of an unskilled witness has been accepted upon the subject of blood is seen in the evidence given in 1682 at the trial of Thompson, Pain and Farwell for libel.

The libel arose out of the earlier trial in 1679 of Robert Green and others for the murder of Sir Edmund Godfrey, who had been waylaid and apparently strangled. This trial was one of those arising out of the so-called Popish Plot, and upon the evidence of Titus Oates, Miles Praunce and others the prisoners were convicted and executed.

Subsequently a letter to Mr. Praunce appeared in The Loyal Protestant Intelligence, which sought to make out that false evidence had been given at the murder trial, and that Sir Edmund Godfrey had not been strangled at all, but had committed suicide.