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Using DNA to solve crime without suspect's DNA

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Kense Report 2 Oct 2021 10:32

The following item on YouTube describes how DNA was used to solve an old murder case even though the murderer's DNA was not on any accessible database (to match with the DNA found at the crime scenes)

This week's edition of the BBC's Click, on iplayer,, also includes a similar story about another murder solved by the same technique.

Interesting moral aspects of using DNA in this way.


JoyLouise Report 2 Oct 2021 11:56

All power to their elbows, Kense, as far as I’m concerned.


PatinCyprus Report 2 Oct 2021 16:13

On GEDmatch you are asked if you want to help the police via your DNA. You have to opt in if yes.


Kense Report 2 Oct 2021 19:22

The point is that they find a number of (opted in) DNA matches with that from the crime scene. They then form trees for those people from publicly available sources to find a common ancestor. They then complete the tree for the descendants of that ancestor which should limit the number of suspects remaining.

What is in contention is the that by opting in you are effectively opting in your cousins without their knowledge or permission.


PatinCyprus Report 2 Oct 2021 20:03

it's only for serious crimes so they deserve to get caught :-D


Bobtanian Report 4 Oct 2021 18:54

AH! Pat,

at the moment, maybe, but in the end.......Needs Must!!


Kense Report 31 Oct 2021 08:17

Another video on the topic


JoyLouise Report 31 Oct 2021 10:29

I don't care about how villains are caught as long as undeniable proof is used. If someone stole, say, a computer from my home, I'd be happy for him/her to be caught by DNA matches. Using DNA as proof, the slippery can no longer be quite so slippery.


RolloTheRed Report 1 Nov 2021 11:15

All very well but such usage of DNA can put a relative of the suspect, say a second cousin, in a very difficult position. The second cousin may be unaware or only vaguely aware of the existence of the suspect. The investigation may have placed the 2nd cousin in the suspect's tree but his/her DNA cannot be used in an evidential way without either the co-operation of Ancestry ( not usually given ) et al or of the 2nd cousin. There are planty of reasons why that permission may not be forthcoming. When it is not the investigation tends to put pressure on the 2nd cousin to grant permission.

If the police, MI5/6 and others wish to use DNA as a crime fighting, state security tool, then there should be a proper rules based way in which to do so, not the ad hoc procedures currently used. A good start would be proper training of the police before they start using such methods. That includes rules of disclosure. Incorreclty used DNA is far from perfect as a crime solving tool.


nameslessone Report 1 Nov 2021 12:06

Pressurising a 2nd cousin. That is lazy policing. The dna result would indicate the relationship and a 'dirty' family tree would be drawn up. That is what geneologists do when trying to trace family members.


Caroline Report 1 Nov 2021 12:09

If the use of DNA and trees can point the police in the right direction, and from there they can start searching for more concrete evidence to convict then I'm all for it.


nameslessone Report 1 Nov 2021 12:54

The story of the Golden State Killer is both frightening and fascinating. I think this may have been the case that changed the laws on access and why gedmatch ask you to opt in/ out.


JoyLouise Report 1 Nov 2021 13:04

I remember my cousin, a forensic scientist, telling me, with a wry smile on his face, how DNA evidence was irrefutable and how it was a game-changer. Once it was discovered, the false statements and dubious alibis faded away in the face of such compelling evidence.

I can see how DNA could be introduced surreptitiously to a crime scene but I think the chance of that happening would be extremely rare and is probably why the forensics people are called to a crime scene immediately.

Rollo, that same cousin travelled to various police forces throughout the country to speak to its use and to train others in various forensic methods so there are rules but if you think a force has not adhered to them, I can think of only one force you may mean - deemed to have more than its fair share of corruption according to my cousin who has done work for them and has come up against some of them in court before and after the use of DNA evidence.


RolloTheRed Report 1 Nov 2021 13:26

DNA is only irrefutable in the case of comparing one person with a given sample, no kith and kind involved. Even then the hows whens and location from which the sample are matters which can be and often are challenged by the defence. As any barrister will tell you DNA is no silver bullet which is why reason why traditional police work goes on. It is far from unusual for evidential DNA to be lost one way or another.

The amount of matching DNA in family trees decreases rapidly as the relationship becomes more extended. This is not so much a problem for family historians but it is for criminal evidence. True there are genealogy organisations that will share DNA with police investigations . One takes uploaded DNA which did not have sharing enabled from the get go. That is unethical.

The second cousin I referred to had been linked to a set of suspects by the Lincolnshire Force, not the London Met. Convictions were secured through trad methods but the degree of pain inflicted on dna partial matches was significant.


JoyLouise Report 1 Nov 2021 13:41

I was not referring to DNA obtained from any other method than finding it at a crime scene.

I can see why police forces may use family tree DNA from genealogical websites but the danger there is not knowing who really gave the DNA. People lie and use other’s names and identities.

Did you second-guess me Rollo? :-D


RolloTheRed Report 1 Nov 2021 15:33

Your life and freedom in their hands.


nameslessone Report 1 Nov 2021 15:45

Wouldn’t that link have been better placed in its own thread..?


RolloTheRed Report 1 Nov 2021 16:18

Not at all.