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Direct testimony & cross examination

Examination of one expert & Cross-examination of the expert
Please stand in the witness box.
Would you like to swear or affirm? Swear. And what holy book would you like to swear upon? The Bible, please. Please hold this in your right hand, and read off the card. I swear by almighty God that the evidence I should give shall be the truth, the whole truth and nothing but the truth. Thank you.
Could you state your full name please? Dr David Ballard. Dr Ballard, I’m going to ask you to speak clearly and at a pace that can be followed by members of the jury. I will be asking you a number of questions that I need you to direct your answers to the jury. Can you tell us what your occupation is please? I’m the senior scientist at DNA Analysis at King’s. And can you tell us what qualifications you have? I have a BSc in physiology from University College London. I have a Master’s of Science in forensic science from King’s College London, and I have a PhD from the University of London. Are you a member of any professional organisations?
I’m a member of the International Society for Forensic Genetics. And what is your particular speciality? My particular speciality is DNA analysis and body fluid identification. Is it correct to say that your laboratory received an exhibit, JG1 recovered from Nelson’s dock? That is correct. Could you describe this exhibit for the court, please? This was a metal bar. It was a right angled metal bar, and at one end, there was a brown substance that could potentially have been blood. Did you perform any tests on this metal bar? We did indeed test this brown substance, and we used a presumptive chemical test to see whether it could be blood, and the results came out that yes, it did indeed presume to be blood.
So on the basis of that presumptive test, what did you do next? We then took a sample from this blood. We extracted the DNA. We then created a DNA profile, and we were then able to see whether it matched to any of the reference samples in the case. And what did you find? We found that the sample of the blood did indeed match to a reference sample from Mr Omar Alvarez. How likely is it that the blood found or the DNA, I should say, at the end of the metal bar, could have come from anyone other than the deceased in this case?
There is around about a one in a billion chance that if a random unrelated man was chosen that he would have the same profile as that of Mr Alvarez. We call that the match probability, is that correct? Yes. And just to confirm one in a billion? Yes, one in a billion. Is it correct that you also received a second exhibit, DGT1? That is correct. Could you tell the court what the nature of that exhibit was? This was a swab that had been taken from a substance that was presumed to be blood that was found on some paving a little way away from the crime scene. And again, did you perform a series of tests on that swab?
We did perform a series of tests. Again, we used presumptive chemical test to see if it was blood, and we did indeed get a positive result suggesting it was blood. We then took a DNA sample and produced a DNA profile. And what results did you obtain from that DNA profile? When the DNA profile was compared against the suspect’s DNA profile, we once again found that there was a one in a billion chance for if we took an unknown, unrelated individual, that they would have this same DNA profile. What conclusion did you draw from that match probability?
The conclusion we would draw is that there is strong support that they swab taken from the paving segment was indeed blood, and that it came from the defendant. Thank you. I’m sure that my friend has some questions to ask you.
Dr Ballard, your evidence is that the blood found on the metal bar at the crime scene came from the deceased. Is that correct? That is correct. And your tests did not find a DNA profile or indeed any other biological material belonging to the defendant on the metal bar. Is that correct? That is also correct.
And the only DNA profile of the defendant that you found in your tests was on the blood swabbed from the paving stones, is that correct? That is correct.
Dr Ballard, are you able to help us understand where the metal bar was found at the crime scene in relation to the blood on the paving stones? So, the metal bar was found at the crime scene about 20 metres away from the victim, from the information I’ve been given. The blood spots on the pavement were found about 30 metres in the other direction from the victim.
Did you, in your tests, attempt to ascertain the length of time that the blood was present on the paving stones? We did not.
So at this stage, is it correct that there is no way of knowing whether or not the blood on the steps was deposited before the blood was deposited on the metal bar, at the same time or indeed afterwards? That is correct. At the moment, we have no reliable test that will give us that information.
The defendant’s evidence is that he passes by Nelson’s dock in Rotherhithe every day on his daily jog. He says that on one occasion, he suffered a nosebleed, which caused droplets of blood, of his blood to fall on the paving stones.
In your opinion, Dr Ballard, is this explanation consistent with the blood droplets matching the defendant’s found at the scene? There are various variables that we need to take into account here. For example, if it’s rained, et cetera, but this is indeed a plausible reason as to why the blood drops could have been found on the paving stone. Thank you, Dr Ballard. Those are my questions. If you could wait there now, my learned friend may have some re-examination. No re-examination, Your Honour.

This video will show you the testimony of an expert witness in court, and their cross-examination.

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