The Court of Appeal’s rejection of Lucy Letby’s application for leave to appeal against her convictions deals with issues of expert witness credibility, independence and expertise.
It also covers the sufficiency of the scientific foundation for the area of expertise and the way in which expert evidence is made available for the Court to consider.
This article analyses the judgment to illustrate how expert evidence is scrutinised in the criminal courts, how experts can be challenged, and the difference between the admissibility of evidence and the consideration of the weight to attach to it.
It does not seek to examine every part of the Court’s ruling. The full judgment can be accessed at: Letby v R [2024] EWCA Crim 748.
The background
Following a trial which began in October 2022, Letby (the applicant) was convicted in August 2023 of seven counts of murder and seven of attempted murder of infants at the neonatal unit at the Countess of Chester Hospital.
She was acquitted on two further counts of attempted murder and the jury was unable to agree on a further six counts of attempted murder.
Leave to appeal her convictions was refused by the single judge and she renewed her application before the full Court of Appeal (CA).
None of the grounds of appeal advanced was found to have any merit and so leave to appeal her convictions has been refused.
The prosecution case
The case was that, between 2015 and 2016, the applicant harmed babies in her care with the intention of killing them. The means of harm varied: causing air embolus by introducing air via intravenous lines; forcing air into the abdomen via nasogastric tubes; force feeding milk; poisoning by administering insulin; physical trauma.
The applicant alone was present on the unit at the time of all the deaths and deteriorations.
The prosecution evidence included expert witness opinions as to possible causes of death; the medical professionals involved at the unit; the applicant’s shift patterns; the records of the babies concerned.
It was alleged that the applicant had falsified some of the records to cover her tracks and that she had taken home more than 200 handover sheets.
Applicant’s grounds of appeal
- The judge was wrong not to direct the jury to disregard the evidence of the main prosecution expert witness, Dr Evans;
- The judge was wrong to reject the submission of no case to answer at the close of the prosecution case;
- The judge was wrong to direct the jury that they did not have to be sure of the precise harmful acts done in order to convict;
- The judge did not take the right course in addressing a jury irregularity during the trial;
- Leave to admit fresh evidence in the form of two reports from a neonatologist, Dr Shoo Lee, to address the defence assertion that the prosecution experts were wrong to diagnose air embolus on the basis of a research paper;
- The effect of the evidence of Dr Lee, together with the weaknesses of the scientific evidence to prove air embolus, would render nine of the convictions unsafe and undermine the safety of the other five convictions.
The police investigation
Following an internal review of the deaths, and the suspension of the applicant from nursing duties, the police began an investigation in May 2017. Dr Evans, a retired paediatrician, was asked to review initially 33 sets of clinical records involving death or deterioration of an infant on the unit and then a further 28 sets of records.
He was asked to provide an opinion on the cause of the collapse of each baby.
He was the lead expert during the investigation. He advised the police to seek further expertise from the fields of histopathology; paediatric radiology; paediatric haematology; paediatric endocrinology; paediatric neuroradiology and paediatric surgery.
His work was peer reviewed by Dr Bohin, a consultant neonatologist.
Issues with the evidence of Dr Evans
On appeal, the applicant argued that Dr Evans’ evidence should have been excluded from the jury’s consideration because he was not a neonatologist; he had not been in full time practice since 2009; most of his current work was purely as an expert witness; he could not be considered sufficiently independent because he had been part of the original investigation; his evidence was not sufficiently reliable to be admitted; he had been the subject of previous adverse judicial comment.
The CA rejected all of those arguments.
(i) Paediatrician not a neonatologist (see paras 113 – 115 of the judgment)
He was appointed a consultant paediatrician in 1980; he had been trained in neonatology although, at the time, this was not a specific sub-specialty, hence he was never a consultant neonatologist; he set up a neonatal intensive care service in Swansea; he designed a new neonatal unit in 1990. The CA found him to be a “highly experienced consultant paediatrician” with “decades of clinical hands-on experience with neonates”.
“He certainly had sufficient knowledge to render his opinion of value; he had expertise that was capable of assisting the jury and was unarguably able to provide evidence with regard to neonates on matters within his expertise, but beyond the experience of the jury”.
(ii) Investigator not expert witness (see paragraph 116)
This argument criticised the approach taken by Dr Evans. The contention was that, as he had been involved in the investigation originally carried out by the police, he could not be sufficiently independent to be capable of being an expert witness at trial. The CA rejected that argument.
“The single judge said, and we agree, that the judge was fully entitled to conclude that the approach of Dr Evans to his task was reasonable and did not amount to partiality or lack of independence, nor was it unreasonable for Dr Evans thereafter to provide some direction and structure in relation to identified cases. To the extent that he was acting as an investigator or director of the investigation, he was not doing so in a way that precluded him from being an expert witness in the case.”
(iii) Evidence not sufficiently reliable to be admitted (see paras. 117-120)
The CA made two observations here. First, that Dr Evans’ evidence was provided without him being given access to the other circumstantial material, so it was uninfluenced by matters outside his expertise and knowledge. Second, his opinions were independently corroborated by other expert witnesses.
The applicant criticised the way in which he gave his evidence. It was contended that some of his answers were too lengthy; that he was argumentative with defence counsel; that he appeared irritated by some of the challenges made to him; that he seemed dismissive of some lines of questioning.
The trial judge, who had seen Dr Evans give evidence over a period of seven days, accepted that there were some valid comments to be made about his manner in the witness box; both he, and the CA, noted the intensity of the cross examination and challenge which he underwent and that there were times when the same matter was being put to him again and again.
The trial judge and the CA both held that the manner in which the witness responded to cross examination was purely a matter for the jury to consider in assessing his credibility and the weight they chose to attach to his evidence; there was nothing about how he conducted himself in the witness box which could have led to his evidence being excluded.
(iv) Previous adverse judicial comment (see paras.101 and 122)
A CA judge in a previous, unrelated, case had criticised a document written by Dr Evans as being “tendentious and partisan”. When challenged on this, Dr Evans pointed out that this was not in fact an expert witness report for court, but a letter to solicitors in a care case. It had been used by them without his knowledge or consent in applying for permission to appeal.
The criticism was put to him; he had not been aware of it before; he explained his understanding of the context; the matter was left for the jury to consider. The CA found nothing wrong with that approach.
Issues with scientific basis for air embolus as a mechanism of harm (see para. 140)
This argument went to the heart of the issues dealt with in Ch.7.1.1-5 of the Criminal Practice Direction 2023. The Practice Direction sets out the factors which the court takes into account when determining the reliability of expert opinion.
The CA rejected the argument that the level of scientific knowledge about air embolus was “so limited that no reliable expert evidence at all can be given about it”. On the evidence, there was no dispute that air embolus can occur in neonates. Research is limited and the occurrence is rare. Nevertheless, the nature of air embolus, its possible causes, the consequences of it, the biological mechanism of how it can lead to death and the signs and symptoms, are all within the knowledge of experienced neonatologists and paediatricians.
“Although their direct clinical experience of air embolus in neonates was inevitably very limited, each of the prosecution's expert witnesses was well qualified in their respective fields to give the evidence which they gave.”
How expert evidence is made available to the court (paras. 5 and 6)
It was open to the defence to call expert evidence of their own. They did not do so. They did instruct a number of experts and serve their reports on the prosecution, but they did not call any expert witness evidence at trial.
The CA noted that, “the entirety of the defence evidence consisted of the applicant’s own testimony” as well as that of an estate plumber (his evidence was not related to any date or time relevant to the counts on the indictment).
Prosecution witnesses were cross examined “robustly” and “serious allegations” were put to them.
Allegations put in cross examination are not, in themselves, evidence.
The CA quoted the trial judge’s directions on this to the jury:
“So where a witness agrees with a proposition in a question then it is the reply of the witness that becomes the witness's evidence. Where a witness does not accept the factual proposition in the question then the question itself is not evidence.”
In the trial, the result was that the prosecution expert witnesses were challenged strongly by the defence; but the points made in the challenge could only become evidence in the case if, either the defence called their own witnesses who could then provide that evidence, or the prosecution witnesses accepted the points made in the challenge.
The net effect was that there was no evidence put before the jury which could contradict the prosecution’s expert evidence.
Conclusions
How is expert evidence scrutinised in the criminal courts?
It will be done, and should be done, forensically. The spotlight is pointed at the scientific foundation for the area of expertise and at the expert’s particular qualification to provide an opinion within that area.
How can expert witnesses be challenged?
Robustly, relentlessly and in forensic detail.
Admissibility and weight of evidence
The issue of admissibility (whether or not evidence is put before the jury) is a question of law which is dealt with by the judge. If they rule that the evidence is admissible, it is then considered by the jury. The ruling to admit the evidence can be challenged on appeal to the CA.
The issue of the weight to give to any evidence is a matter entirely for the jury. Counsel can seek to persuade them to take one view or another of the evidence. The judge must leave it up to the jury. What weight the jury has in fact given to each piece of evidence might be inferred from the verdict that they reach.
The jury’s decision is not appealable, only the judge’s directions on the law.
In summary, the CA’s ruling is an informative and useful exploration of how the criminal courts deal with issues of expert evidence. An expert giving evidence in the criminal justice system should be familiar with the courts’ approach and be ready to deal with the inevitable challenges, as Dr Evans was in this case.
Author: Nick Deal
23 July 2024