Study identifies key traits and methods of serial killer nurses Serial killer nurses often gain notoriety among their colleagues before their crimes are exposed because they hold detailed morbid conversation with grieving relatives, new research into the characteristics of so-called "angels of death" has found. Criminologists studying the traits of healthcare professionals who became multiple murderers found that most craved attention, switched hospitals frequently, had disciplinary problems and liked to talk about death or exhibited "odd behaviour when someone dies." The research, by criminologists from Birmingham City University, examined 16 convicted male and female nurses who murdered within a hospital and who, between them, have killed more than 120 patients. They found that poisoning was the most common way to murder with the research stating that the importance of monitoring access to drugs within hospitals cannot be overestimated. An insulin overdose was the most common method, used by a quarter of the healthcare serial killers (HSKs), with other medications and substances including muscle relaxants, opiates, potassium and bleach also used. In only one case, that of English nurse Beverley Allitt, was poisoning combined with other methods, namely suffocation. The research identified a series of "common criminological and socio-demographic characteristics" prevalent in offenders, which also included difficulties in developing personal relationships, a history of mental instability, a likelihood of switching hospitals frequently and a preference for nightshifts, presumably to minimise the likelihood of being caught. Among the British offenders they examined were Benjamin Geen, who in 2006 was convicted of murdering two of his patients and causing grievous bodily harm to a further 15 patients at Horton general hospital in Oxfordshire. Oxford crown court heard the staff nurse from Banbury injected patients with unauthorised lethal doses of drugs which caused them to stop breathing and also how he revelled in the thrill of trying to revive his patients. Allitt, was found guilty of the murder of four children in 1993 along with the attempted murder of a further three children and of causing grievous bodily harm with intent on a further six children. The 46-year-old is serving 13 life sentences for the crimes committed in the Grantham and Kesteven general hospital where she was a nurse. However, Britain's most prolific serial killer, Harold Shipman who killed at least 250 of his patients over 23 years is not included in the cases examined. Instead researchers only analysed nurses who murdered within a hospital setting, omitting doctors like Shipman who were serial killers and those primarily employed within nursing homes, rather than hospitals, clauses that reduced the number of cases from 42 to 16. Another British "medical murderer" included in the study was nurse Colin Norris, convicted in 2008 of murdering four elderly women and attempting to kill a fifth, by poisoning them with insulin. The Criminal Cases Review Commission (CCRC), which investigates possible miscarriages of justice, is currently examining evidence which challenges the 37-year-old's conviction. Despite no direct evidence linking Norris to any of the patients, he was on shift when they all had similar hypoglycaemic episodes - when the blood sugar drops to dangerously low levels. The criminologists say that their study corroborates claims of innocence by Norris, saying that their study shows that just because a nurse is on duty when deaths occur is not sufficient by itself to indicate guilt. The study, to be published in the Journal of Investigative Psychology Journal of Investigative Psychology and Offender Profiling, urges that "attendance data should be treated with caution as evidence in the investigation and prosecution of suspected HSKs. A spike in the numbers of deaths on the shifts of a suspected HSK may well be an indicator of wrongdoing. However, this should only be used in combination with other types of evidence, which may include some of the common red flags we discovered in our sample. David Wilson, professor of criminology at Birmingham City University, said "The authorities and law enforcement agencies should look for a cluster of factors - red flags - to indicate if there is a murderer at work. Healthcare serial killers are an extremely rare phenomenon, contrary to public perception. Wilson has also sent the research to Greater Manchester police ahead of the Stepping Hill hospital trial, due to begin at the start of next year. Nurse Victorino Chua, 48, is accused of poisoning hospital patients, including three counts of murder. Manchester crown court has heard that the case involved the alleged poisonings of 21 patients at the hospital in Stockport. Most of the killers identified by the criminologists come from the US with their number including male nurse Charles Cullen, 24, who may be the country's most prolific serial killer and who confessed in 2004 that he killed up to 40 patients during the course of his 16-year nursing career, although some have estimated that he may have killed up to 400 patients in many different hospitals. Of the 16 offenders identified by the criminologists 10 had a history of mental instability or depression while half appeared to have a personality disorder.