The fact that a doctor had killed 15 patients sent a shudder through the medical community, but this was to prove insignificant in light of further investigations that delved more deeply into his patient case list history.A clinical audit conducted by Professor Richard Baker, of the University of Leicester, examined the number and pattern of deaths in Harold Shipman's practice and compared them with those of other practitioners. It found that rates of death amongst his elderly patients were significantly higher, clustered at certain times of day and that Shipman was in attendance in a disproportionately high number of cases. The audit goes on to estimate that he may have been responsible for the deaths of at least 236 patients over a 24-year period.Separately, an inquiry commission chaired by High Court Judge, Dame Janet Smith, examined the records of 500 patients who died whilst in Shipman’s care, and the 2,000-page report concluded that it was likely that he had murdered at least 218 of his patients, although this number was offered by Dame Janet as an estimation, rather than a precise calculation, as certain cases presented insufficient evidence to allow for certainty.The commission further speculated that Shipman might have been “addicted to killing”, and was critical of police investigation procedures, claiming that the lack of experience of the investigating officers resulted in missed opportunities to bring Shipman to justice earlier.He may in fact have taken his first victim within months of obtaining his licence to practise medicine, 67-year-old Margaret Thompson, who died in March 1971 whilst recovering from a stroke, but deaths prior to 1975 were never officially proven.Whatever the exact number, the sheer scale of his murderous activities meant that Shipman was catapulted from British patient killer to the most prolific known serial killer in the world. He remained at Durham Prison throughout these investigations, maintaining his innocence, and was staunchly defended by his wife Primrose and family. He was moved to Wakefield Prison in June 2003, which made visits from his family easier.On 13 January 2004 at 6 am, Shipman was discovered hanging in his prison cell at Wakefield, having used bed sheets tied to the window bars of his cell.There remains some mystery about the whereabouts of his remains, with some claiming that his body is still in a Sheffield morgue, while others believe that his family have custody of his body, believing that he may have been murdered in his cell, and wishing to delay his interment pending further tests.