Lucia de Berk case

Suspicions and investigation

Colleagues noticed that patients often died while De Berk was on duty, particularly after a five-month-old baby turned blue and died unexpectedly despite doctors saying her condition was improving. A post-mortem indicated foul play, prompting an investigation into deaths between 1997 and 2001 at three hospitals in The Hague. Evidence of poisoning through tranquilizer overdose was found in some cases, though many deaths had no firm explanation. De Berk was charged with killing thirteen patients and attempting to kill five others using tranquilizers, painkillers, and potassium.

Trial

De Berk's trial began in September 2002. The prosecution presented diary entries they claimed showed she was obsessed with death, and noted she had tried to burn the diaries when the investigation started. A toxicologist, an FBI profiler, and a statistician testified for the prosecution. Traces of poisonous toxins were found in the blood of three exhumed children, including the five-month-old baby.

Police found books about crimes and murders in her home, such as Bad Blood: the Thanatos Syndrome Serial Murderer and Corpus Delicti: the 30 Most Notorious Crimes of the Low Countries. De Berk had forged a Canadian diploma to qualify for medical training and faced additional charges for falsification and book thefts; she admitted lying about her credentials and stealing books, medicine, and patient files. The prosecution argued she killed or attempted to kill patients by unnecessarily increasing drug dosages or giving hard-to-detect drugs.

One trial judge noted a pattern: De Berk would alert colleagues to a problem, then a crisis occurred. De Berk denied the charges, blaming other staff or equipment, and said her diary entries were misinterpreted—her reference to a compulsion was about laying Tarot cards for patients. She testified that the death of a six-year-old Afghan boy from a lethal dose of sleeping medication was strange but she did not know how it happened. Her defence argued she was present at deaths because she was concerned for her patients.

Doubts

A statistician testified that the odds of all incidents coinciding with De Berk's shifts were 342 million to one, but this claim was later criticised. The appeals court upheld the conviction despite these doubts. Philosopher of science Ton Derksen and his sister Metta de Noo-Derksen wrote a book questioning the court's reasoning and the medical and statistical evidence. The defence showed that De Berk could not have been involved in several cases due to administrative errors that overlooked her absence for days.

All deaths except the last had been registered as natural; even that one was initially thought natural by doctors before being reclassified. A Dutch professor of criminal law, Theo de Roos, stated that statistical evidence was of enormous importance and that a conviction without it seemed unlikely. Philip Dawid, Professor of Statistics at the University of Cambridge, criticised the prosecution's statistical evidence as unprofessional and based on simplistic assumptions. The case was discussed in a 2007 Nature article by Mark Buchanan.

Case reopened

On 17 June 2008, Advocate-General G. Knigge requested the Supreme Court to reopen the case, and on 7 October 2008 the court agreed, acknowledging new facts that undermined earlier evidence. At the third appeal, doubt was cast on evidence of high digoxin levels in one child's blood, which had been key to the 2004 conviction. Digoxin levels in autopsy blood are naturally higher than in living patients because heart cells die and release the drug; the blood sample was squeezed from gauze left inside the body after two autopsies, and evaporation increased the concentration.

The presence of digoxin-like immunoreactive substances (DLIS) in infants complicated testing, as the tests could not distinguish between digoxin and DLIS. A Strasbourg laboratory found 7 milligrams of digoxin per litre, below the threshold for poisoning, and other medical findings showed no evidence of poisoning. The opportunity to poison was also flawed: the monitor was disconnected for 28 minutes, but a doctor's examination was logged at 1:00, and log sheets always recorded on the hour or half hour.

A reconstruction showed the disconnection was for the examination itself, and digoxin kills within an hour, so it would have had to be administered during that examination.

Did You Know?

• Sceptics of British nurse Lucy Letby's murder convictions have cited the De Berk case as precedent.