Related Sector: Expert Witness

Anyone following the Post Office Horizon IT Inquiry will know that it has emerged that contradictory evidence was provided by the prosecution expert witness at trial. Against that background, it is a good time to reflect again on the role and duty of expert witnesses in the criminal justice system.

The full story has not yet come out – that is the purpose of the Inquiry, after all. The reason for this article is to comment on some of the issues which are coming before the Inquiry, namely:

-       the instruction of expert witnesses

-       their duty to the court

-       commentary on expert evidence by prosecution lawyers

The background, very briefly, is as follows. The Post Office (“PO”) had instructed an expert witness, “GJ”, to comment on the operation and integrity of the Horizon software system, designed by Fujitsu. GJ was a Fujitsu employee.

In a witness statement dated 8th October 2010, GJ apparently stated that there were no cases where PO branch accounts could be altered remotely without the sub-postmaster’s knowledge. That witness statement was used in the trial and conviction of Seema Misra – her conviction was subsequently quashed in 2021.

In an internal report, dated 29th September 2010, GJ had apparently stated that one way to fix the bugs in the Horizon system was to alter the PO branch data remotely.

In the case of Seema Misra, that possibility was not made known to the defence, or to the jury.

It is also on record that prosecuting counsel asked if GJ could make some changes to his witness statement - in order to avoid making the Horizon system look unreliable. Some of those changes were incorporated into the witness statement of October 2010.

What do the Criminal Procedure Rules (“CrPR”) and the law say?

  1. Instruction of expert witnesses

Those who instruct expert witnesses have an obligation to ensure that they are aware of their duty as experts (discussed below); in addition, prosecution lawyers have an obligation to ensure that the expert understands their duties of disclosure of unused material.

Instructing lawyers should at least draw their expert’s attention to CrPR 19 (“Part 19”) and Chapter 7 of the Practice Directions 2023 (“Chapter 7”).  There should be a discussion around the requirements placed upon the expert witness to ensure that the expert understands them and will comply with them.

Prosecution lawyers must also tell the expert about the CPS Guidance for Experts on Disclosure, Unused Material and Case Management (“CPS Guidance”).

Instructing lawyers should be satisfied that the expert will be sufficiently independent to be able to perform their role. Someone who is an employee of an interested party can be engaged as an expert witness as employment is not an automatic bar to instruction. However, careful consideration would need to be given regarding their ability to provide independent, objective evidence. and equally careful discussion with the expert before appointment to ensure that they had understood the role they were being asked to fulfil.

In such circumstances, the expert’s understanding and fulfilment of their duty to the court must be clearly demonstrated.

       2. The duty of the expert witness

The duty is set out in Part 19.2. The duty is stated to be to “help the court to achieve the overriding objective” and that is done by giving opinion which is “objective and unbiased and within the expert’s area or areas of expertise”.

It is expressed as overriding “any obligation to the person from whom the expert receives instructions or by whom the expert is paid”.

The expert must help the court, not their instructing party or employer. They must be objective and unbiased. In other words, their reports must be evidence-based and not seen to build the case for their instructing party.

Implicit within that duty, and explicit within the statement of truth and the oath or affirmation, is that the expert is truthful in all the evidence they provide - written and oral.

Objectivity requires that the expert considers and discusses all the evidence and is not selective in their approach. If the expert is aware of evidence which is relevant, they need to make it available through their report. In essence, they are under a duty to provide the court with the full picture - not just a partial image of the evidence and of their opinion.

When writing a report for court, an expert witness goes on to sign a series of declarations which reflect their knowledge and understanding of, and compliance with, their duty (see Chapter 7). Note that the declarations include specific confirmation that the expert has read Part 19 (and complied with it) and the CPS Guidance (and followed it).

       3. Commentary on expert evidence by prosecution lawyers

This is a very sensitive area. Ultimately, the expert’s evidence must represent their own opinion. The declaration states that they have not included or excluded anything suggested by their instructing lawyers “without forming an independent view” (see declaration paragraph 9).

That implies that while it is legitimate for lawyers to make suggestions, the content of the final report must represent the opinion of the expert alone.

Lawyers can, therefore, explore whether or not the expert can be clearer, or firmer, or stronger in the expression of their opinion. The lawyers can suggest wording which would serve their case better; they cannot tell an expert what to write (to be clear, there has been no evidence of that at the Inquiry); the expert must still put their duty to help the court above all else.

Draft versions need to be saved and may need to be disclosed to the defence as unused material.

It will be interesting to follow the continually emerging story of the PO miscarriage of justice and to see what conclusions the Inquiry eventually makes about the instruction and involvement of expert witnesses and the role played by the PO lawyers, internal and external.

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