 Heath originally told his counsel, J. D. Casswell KC, to plead guilty, but when Casswell questioned this, he said, "All right, put me down as not guilty, old boy".Casswell chose not to call him to give evidence, and relied on the defence of insanity, calling William Henry de Bargue Hubert, an experienced criminal psychiatrist, to testify as an expert witness.Hubert testified that Heath knew what he was doing but not that it was wrong, but the prosecution easily destroyed Hubert's argument