Lucia de B must be retried

Lucia de Berk, the dutch nurse convicted to life imprisonment for the allegated murder of a number of patients should be retried.

The so called Posthumus commission in its report of today stated that the entire case is fraud with tunnelvision from the DA’s office. From the start they were convinced that Lucia de B was guilty and their entire evidence gathering was based on that. Any evidence pointing to her innocence was disregarded or discarded.

The commission was especially critical towards the statistical ‘evidence’ in the case as only 1 statistician calculated the chance that Lucia was ‘not guilty’ on 1 in 340.000.000 This calculation was not shared by other, more scientifically renowed statisticians, who calculated it at 1 in 40 or 1 in 8. The statistics never should have been allowed as evidence, the Posthumus commission stated in its report.
There were no murders

Lucia de Berk (born 1961), in the Dutch media generally called Lucy de B. or Lucia de B., is a Dutch nurse who was sentenced to life imprisonment in 2003 for four murders and three attempted murders on patients in to her care. After an appeal she was convicted in 2004 of seven murders and three attempts. Her conviction is controversial among the media, scientists and the public

As a result of an unexpected and unexplained death of a baby in the Juliana Children’s Hospital (JKZ) in The Hague, The Netherlands, on 4 September 2001, earlier deaths and resuscitations were scrutinized. Between September 2000 and September 2001 there appeared to have been nine incidents, which earlier had all been thought unremarkable but now were considered medically suspicious. Lucia de Berk had been on duty at the time of those incidents, responsible for patient care and delivery of medication. The hospital decided to press charges against the licensed child nurse.

Life sentence

On 24 March 2003 de Berk was sentenced by the court in The Hague to life imprisonment for the murder of four patients and for the attempted murder of three others. The verdict depended in part on a statistical calculation, according to which, allegedly, the probability is only 1 in 342 million that a nurse’s shifts would coincide with so many of the deaths and resuscitation purely by chance. De Berk was however only sentenced in cases where, according to some medical expert, other evidence was present or in which, again, according to some medical expert, no natural causes could explain the incident.

In the appeal on 18 June 2004 de Berk’s conviction for the seven murders and three attempted murders was upheld. The crimes were supposed to have taken place in three hospitals in The Hague; the Juliana Child Hospital (JKZ), the Red Cross Hospital (RKZ) and the Leyenburg Hospital where de Berk had worked earlier. In two cases the court concluded that there was proof that de Berk had poisoned the patients. Concerning the other cases the judges considered that they could not be explained medically, and that they must have been caused by Lucia de Berk, who was unable or unwilling to give a reason why she was present on all those occasions. The idea that only weaker evidence is needed for the subsequent murders after two have been proven beyond reasonable doubt has been dubbed chain-link proof by the prosecution and adopted by the court. At the 2004 trial, de Berk also received TBS (terbeschikkingstellen, psychiatric detention with coerced psychiatric treatment), which is a strange addition to a life sentence, when the suspect did not plead mental illness as cause of her crimes (she denied committing them), nor did the state criminal psychological observation unit find any evidence of this. The Court found this so far unique sentence necessary, because of the likelihood that she would otherwise return to society after the standard release from life imprisonment after 20 years detention. This way de Berk would remain detained for psychiatric treatment and prevented from ever returning to society.

Important evidence at the appeal was to be the statement of a detainee in the Pieter Baan Center, the criminal psychological observation unit, at the same time as Lucia de Berk, that she had said during outdoor-exercise: “I released these 13 people from their suffering”. However, during the appeal, the man withdrew his statement, saying that he had made it up. The news service of the Dutch Broadcasting Foundation (NOS), and other media that followed the process, considered the withdrawal of this evidence as a huge setback for Public Prosecution Service (OM). This witness statement was the only hard evidence, and it had vanished. A series of articles appeared over the following years in several newspapers, including Vrij Nederland and the Volkskrant, doubting the safety of the conviction. It was suggested that the prosecution had manipulated evidence and the judges had drawn the wrong conclusions.

The case was next brought to the Supreme Court, which ruled on 14 March 2006 that it was incorrect to combine life imprisonment with subsequent psychiatric detention. Other complaints were not taken into consideration, and the evidence from the Strasburg analysis was not considered relevant. The Supreme Court gave the matter back to the Court in Amsterdam to pass judgement again, on the basis of the same factual conclusions as had been made before. Some days after the ruling of the Supreme Court, de Berk suffered a cerebral infarction and was admitted to the hospital of Scheveningen prison. On 13 July 2006, as expected, de Berk was sentenced by the Court of Appeals in Amsterdam to life imprisonment, with no subsequent detention in psychiatric care.


A few persons continued to express doubts about the conviction of de Berk. Philosopher of science Ton Derksen, and his sister, geriatrician Metta de Noo-Derksen, wrote the (Dutch language) book “Lucia de B: Reconstruction of a Miscarriage of Justice” [1]. The doubts are related to the chaining-evidence argument used by the court and the medical and statistical ingredients.

Chaining-evidence proof

Of the seven murders and three attempted murders finally attributed to de Berk by the court, only two were considered by the court proven by medical evidence. According to the court de Berk had poisoned these two patients. The court then applies a so-called chaining-evidence argument. This means that if the several (attempted) murders have already been established beyond reasonable doubt, then much weaker evidence than normal is quite sufficient to establish that a subsequent eight “suspicous incidents” are indeed suspicious and in fact are murders or attempted murders carried out by de Berk.

This is controversial, because for the two murders found proven by the court, many experts still did not exclude a natural cause of death. In the case where digoxin poisoning was alleged, and supposedly detected by independent measurements in two Dutch laboratories, the (same) method used in those laboratories did not exclude that the substance found was actually a related substance naturally produced by the body itself (i.e., this could be a false positive, and the two measurements are not better than one). The Strasburg laboratory used a new method, sometimes refered to as the gold standard, a test of high specificity and sensitivity, and it did not reveal presence of any digoxin. In the other case, the intoxication could well have been an overdose caused by a faulty prescription. For both children, the question moreover remained, how and when de Berk was able to administer the poison. Regarding the digoxin case, the prosecution gave a detailed reconstruction of the timing. However, other parts of the evidence, discarded by the prosecution, showed by the timestamp on a certain monitor that at the alleged moment of poisoning Lucia was not with the patient at all, and in fact the specialist and his assistant were with the patient at that time.

The prosecution initially charged de Berk of causing thirteen deaths or medical emergencies. In court, the defense was able to show definitively that de Berk could not have been involved at all in several of these cases. For instance, she had been away for several days; the idea that she was there was due to administrative errors. Furthermore, it should be pointed out that all deaths had been registerd as natural, with the exception of the last event. Even that last event was initially thought natural by the doctors responsible for the child, but within a day, on being connected with Lucia and her repeated presence at recent incidents by other hospital authorities, it became an unnatural death.

Statistical proof

There is no hard proof against de Berk. She was not caught “red-handed”, and has always denied guilt. Among other things, the court made heavy use of statistical calculations to achieve its conviction. The chance of a nurse working at the three hospitals being present at the scene of so many unexplained deaths and resuscitations is estimated at one in 342 million. The relevance of this number is controversial. It seems that the hospital and the OM had decided in advance that the deaths had been caused by a nurse; and still insist exclusively on this line of enquiry.

The multiplication of probabilities concerning three departments was wrong: if one wishes to combine p values (right tail probabilities) of the statistical tests based on data from three separate wards, one must introduce a correction according to the number of tests, as a result of which the chance becomes one in a million (Fisher’s method for combination of independent p-values [2]). In the summing up after the appeal, the Court of Justice no longer reported the results of a probabilistic calculation. However, the judge implicitly continued the use of the statistical data. It was considered clear that so many incidents could not have occurred by chance. Derksen has reported to the Posthumus II committee, chaired by Y. Buruma, that the number of incidents that occurred during de Berk’s shifts were too large, and the numbers for other nurses were too small. Correcting those figures, increases the chance to about one in fifty. Taking account also of some innocent variation in the rates of incidents experienced by different nurses, as suggested earlier by A.F. de Vos, the chance becomes one in nine. In the judges’s summing-up, evidence is selected from many different medical experts, in order to argue that each of the incidents to be attributed to Lucia was indeed an unnatural death or near-death. Sometimes specialist A is preferred above specialist B, sometimes the other way around, sometimes another, C. In that case, C is arguably the most expert person, because he alone considered the incident unnatural. In another case there is only one expert who considers the death unnatural. He actually stated that he only has this opinion because Lucia was present and she had been present at so many other incidents. This is not mentioned in the judge’ conclusion.

The use of probability arguments in the de Berk case was discussed in a 2007 Nature article by Mark Buchanan[3]

The court needs to weigh up two different explanations: murder or coincidence. The argument that the deaths were unlikely to have occurred by chance (whether 1 in 48 or 1 in 342 million) is not that meaningful on its own – for instance, the probability that ten murders would occur in the same hospital might be even more unlikely. What matters is the relative likelihood of the two explanations. However, the court was given an estimate for only the first scenario.

The Diary

De Berk’s diary also played a role in her conviction. On the day of death of one of her patients (an elderly lady in a terminal stage of cancer) she wrote that she had ‘given in to her compulsion.’ She wrote on other occasions that she had a ‘very great secret,’ and wrote that she was concerned about ‘her tendency to give in to her compulsion.’ De Berk stated that this referred to her passion for reading tarot cards, whereas the court decided it was evidence that she had euthanized the patients. De Berk explains that she did this in secret, because she did not believe it appropriate to the clinical setting of a hospital. According to the court the reading of cards does not accord with a compulsion nor with perhaps an expression of fatigue as she described it at the time. The daughter of de Berk, Fabiënne, explained in an interview on the television program Pauw & Witteman that some of her mother’s notes in the diaries are ‘pure fiction,’ which she wanted to use for a thriller.

The Dutch Forensic Institute (NFI) report

After the appeal procedings were closed, but before the judges delivered their verdict, the Public Prosecution Service received, via the NFI, a report from a prestigious forensic laboratory in Strasbourg. This had been requested by the NFI who had hoped that it would support the hypothesis of digoxin poisoning. In fact, the NFI wrote to Strasburg that they were hoping for a miracle. The report subsequently lay in a drawer of the NFI for two years, but it did turn up in time for the final evaluation of the case before the Supreme Court. According to the Public Prosecution, the report contained no new facts, but according to de Berk’s defence the report proved that there was not a lethal concentration of digoxin in the first case. The Supreme Court accepts the facts reported by the judges at the appeal court, and is concerned only with jurisprudence and correctness of the sentence, given those facts. The report therefore was not admitted to the final considerations of the sentence given to Mrs. de Berk.

Posthumus II Commission

Ton Derksen submitted his and Metta de Noo’s research on the case, to the Posthumus II Commission. This ad hoc, non permanent, commission examines some selected closed cases and looks for evidence of errors in the police investigation regarding “tunnel-vision” and misunderstanding of scientific evidence. Derksen pointed out that the medical experts who had ruled out the possibility of death by natural causes had not been given all relevant information, that the hypothesis of digoxin poisoning was disproven, in particular by the Strasburg analysis, and that the statistical data was biased and its analysis incorrect, and the conclusions drawn from it invalid. The commission announced on 19 October 2006 that this is one of the few cases it will consider in detail. Three wise men, recruited by the Public Prosecution service from the full Posthumus II committee, are considering the following matters, though they have been instructed to focus on possible blemishes in the criminal investigation:

  • Whether there were also unexplained deaths when Lucia de Berk was not present, unknown to the public prosecutor,
  • Whether the expert witnesses were given all relevant available information.
  • Whether scientific knowledge now throws a different light on digoxin question.


The Three Wise Men will make no judgement on de Berk’s guilt or innocence but could recommend that her case be reopened. It is now expected that the commission will make its recommendation in October 2007.


3 thoughts on “Lucia de B must be retried

  1. The number was actually 1 out of 342.00.00. And ths statistian was not involved in statistics for more than 30 years. Prof. dr. Gill, president of the Dutch Statistical Society brought it back to one out of nine. Thus when you have ninety thousand nurses, like in the Neterlands, it will happen to 10.000. Thus there are 10.000 serial killers. Would you be so brave and visit a Dutch Hospital. Thus there is some fishy about it.
    A witch trial took place convicting Lucia to life imprisonment with a shred of evidence. There were no facts whatsoever which justified the thought of murder!!, see
    Completely, without any doubt innocent.

  2. Thanks Nico. I already noticed I had made a mistake with the number and thought it was 340 million. As a result of your comment I checked and indeed found 340.000.000 mentioned, so that is how I changed it now. The statiscal chance as it is calculated now, whether that is 1 in 8 or 1 in 40, actually is more like the chance you have of getting a flat tyre while cycling to work.
    Indeed the entire thing is fishy, she should never have been convicted.
    Infact, the statistics were also subject of an article in an international science journal (forgot which one) and they were heavily criticized to say the least.
    I had planned to make a bigger article out of this, but a lot already has been written on it so I will keep it as short news updates. I myself find it a scandal that Albayrak has not taken action yet. Instead of asking questions on the Holleeder stamp, Fred Teeven better asks questions on the deplorable screw-ups in our judicial system.
    Thank you very much for your comments

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