Computer Expert Witness
Graham Dilloway CITP MBCS
Computer Expert Witness

Chartered IT Professional and Member of British Computer Society

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Member of the Academy of Experts

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Police Interviews

Gaps in Understanding

I have read the transcripts of well over 200 police interviews where the subject of the interview has been evidence recovered from a computer..  The interviews almost always show that the police officers or the suspect or, most usually, the officers and the suspect have not fully understood the evidence from the computer. 

I usually find that the police officers and the suspect manage to mislead each other during these interviews.  In one case, I was asked to look at evidence during the preparations for an Appeal and found that the entire proceedings appeared to be based upon misleading and incorrect admissions by the suspect in interview and that the admissions were made in response to misleading assertions made by the interviewing police officers.  Without the misleading and incorrect admission, there would have been no evidence of any crime.

Police Computer Examination Reports

It have seen hundreds of reports produced by police computer examiners.  These reports usually describe in detail everything that was found during the examination.  The reports usually offer little to explain the findings of the examination.  For example, a report might list dozens of indecent images of children with information about the dates that the pictures were created on the computer and the names of the folders that contained the pictures.    Typically, there is nothing in the report to explain what a person is likely to have done to cause any of the pictures to have been stored on the computer.  I have no idea why police officers are expected to conduct interviews without having been given a proper explanation of the evidence by a computer examiner.

It is well established that finding an indecent image of a child on a computer is not enough to prove guilt.  There must also be evidence that the picture was saved or viewed knowingly and deliberately.  My understanding of the law in this area is discussed in my Appeal Court Judgements essay here ...

Misleading Police Assertions

It is common for the police officers conducting an interview to have a computer examiner's report that lists the indecent images found on a computer.  The report might not identify the pictures as having been deliberately saved by a person or as having been stored automatically by software.  The officers might ask, "Why are there 200 nasty pictures on your computer."  The suspect might have known that there were twenty pictures that he had deliberately saved.  The suspect might not understand why the 180 other pictures were found because these pictures had been created automatically by software and he did not know that they were on the computer.

Typically, a police computer examiner's report only lists indecent images of children.  A report might list twenty pictures as being in a single folder and might not say that the same folder also contained 1,000 other pictures that were not of children.  Interviewing officers might be less sceptical about a denial regrarding the indecent pictures if they knew the full content of the computer and its folders.

Information about the deleted or not-deleted status of pictures is usually in the report available to the officers at the interview.  However, pictures are often not separated into lists of deleted and not-deleted pictures.  I have seen interviews where officers have mistakenly asserted that deleted pictures were readily available to a suspect and that the suspect "must have known" that the pictures were on his computer.

Misleading Suspect Admissions

In police interviews, people want to be helpful and tell the truth (or appear as if they are helpful and are telling the truth).  Typically there is an initial interview immediately after arrest and before any computer has been examined.  During this initial interview, the police often ask, "Will we find indecent images of children on the computer when we examine it?"  Most people do not know about the detailed operation of the software on their computer.  Most people do not know if pictures are automatically saved or deleted or when they are automatically saved and deleted.  I have seen interviews where people say that there might be indecent images on their computer even though they do not know whether the pictures are on the computer or not.  The interviewing officers often treat any suggestion that there "might be pictures" as an admission of some deliberate act and the interview can become a riot of misleading questions and inaccurate answers. 

I am an avid reader of news websites.  When browsing, I often see pictures of the Prime Minister but I have never deliberately saved a picture of the Prime Minister.  I might be asked if a search of my computer would find a picture of the Prime Minister.  My truthful and honest answer would be, "I don't know" because I cannot know if and when a picture was automatically deleted after having been automatically saved.

A suspect might know that he had deliberately saved a handful of indecent pictures of children onto his computer.  In interview, the police might not differentiate between deleted and not-deleted pictures nor between deliberately saved pictures and pictures saved automatically by software and might accuse the suspect of having hundreds of pictures.  A confused suspect might assume that it is he who is mistaken rather than the police and the suspect might admit to having hundreds of pictures.  The confused and incorrect information may persist throughout proceedings and finish with a plea of guilty to possession of two hundred pictures rather than guilty to the true figure of twenty pictures.

Incorrect Charges and Indictments

In my estimation, more than half of the Indictments that I see regarding indecent images of children are "wrong".  A "wrong" Indictment might include Counts of possession of indecent images where the pictures were automatically created by software without the Defendant's knowledge or where the pictures were deleted and inaccessible to the Defendant. 

In one case, I was able to show that three Indictments were "wrong" before the Prosecution eventually produced a fourth version that matched the evidence.  I worked another case where the initial Indictment listed nineteen charges.  This was reduced to three charges when it was shown that sixteen of the Counts related to pictures that were, for example, created automatically by software.

It is my view that one of the factors leading to "wrong" Indictments is misleading information gleaned from police interviews.

I almost never see cases where the Defence pleads guilty at an early opportunity because these cases have no need for a computer expert witness.  It is my expectation that some guilty pleas are based upon misleading police interviews that lead to misleading charges and misleading Trial proceedings and, quite possibly, to excessive sentences.

Preparation for Police Interview

It might be helpful to prepare for a police interview regarding indecent images of children by seeking assurances regarding the exact nature of the evidence recovered by the police computer examiner.

It may be that the interviewing officers could be asked to categorise the pictures listed in any report from the computer examiner.  The categories might be:

It may be that the officers will be unable to provide this information in a timely manner and the interview may go ahead without.  However, it may be that asking the question will forestall any precipitous assumptions by the officers and deter them from making misleading assertions.

I am usually available at any time if it would be useful to call prior to an interview.  My contact information is  here ...

Worst Case Scenario

I was asked to look at evidence as part of the preparation for an Appeal. 

The evidence from the computer was a very small number of pictures.  The accused was asked in interview to explain a document containing pictures that was found on his computer.  The accused explicitly asked the officers if the document was a deleted file and was told that it was not.  In fact, the document was a deleted file that had been automatically created by software and automatically deleted by software while the computer was being used to browse a website.  There was no evidence to show that the document had been accessed by a person knowing the exact nature of its content.

The accused was confused by the assertion that the document was not-deleted because he had no recollection of that specific document having been stored on his computer.  The transcript of the interview contained about two pages of questions and answers where the accused was confused and appeared to both admit and deny knowledge of the document.  It also appeared from the transcript that he might have been confusing the document with another similar document that was not found on the computer.

As is usual, the interview was read to the Court during the Trial.  The Prosecuting Counsel relied heavily on what he said were admissions in the interview because there was no other evidence to show how or why the document came to be on the computer.  It is highly likely that there would have been no charges regarding the pictures in this document without the misleading admissions made as a result of misleading assertions during the interview.

The Appeal relied primarily on other Grounds to do with other evidence that should not have been admitted at Trial.  The Appeal was allowed but the Court did not refer to the lack of evidence in their judgement.

A simple incorrect assertion in interview led to charges that should never have been brought and a Trial that should never have been heard and, eventually, to the Court of Appeal.

Afterword:  The Appeal Court judgement was reported in a local newspaper and the report is grossly wrong about the proceedings and the judgement.  The newspaper appears to have completely misunderstood the evidence.  It seems that once a misleading fuse has been lit, it is hard to put it out.


It may be that, before a police interview, the evidence found on a computer has not been fully explained to the police officers conducting the interview.  Misunderstanding of the evidence can lead to misleading assertions by the police officers and to misleading admissions by a suspect.  It may be that interviews involving indecent images of children would be less misleading if those at the interview knew whether pictures were deleted or not and whether pictures were stored automatically by software or not.