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Julie Reilly
10-19-2011, 12:33 PM
Following on from my previous question.

In the event of a murder victim scratching her killer and then being buried, how long would the DNA evidence in the form of skin scraped from under her nails be viable and traceable?

Drachen Jager
10-19-2011, 06:51 PM
The technology for recovering DNA improves over time, so as the DNA degrades, the technology would probably continue to grow at such a rate that the DNA evidence would never be lost. Certainly not in under 100 years or so.

If she got some of his hairs, they can recover some DNA (enough for use as evidence) from hair strands as long as the hair is intact (possibly thousands of years).

Zelenka
10-19-2011, 06:59 PM
Just got very sidetracked in one of my old textbooks from forensics class... But it very helpfully says that the degradation of the DNA will depend on 'environmental factors' without giving any real statistics as to how long it would take in different soil types etc. From what I understand, if the tissue itself has completely putrefied, then the normal cellular DNA will not give any usable results, so it would depend how long she's been buried, where she was buried, if there was any factor present that may have preserved the body in part (and therefore any other tissue present on the body). However, as Drachen Jager said, DNA evidence from hair rather than skin cells will be viable a lot longer. Mitochondrial DNA has been successfully extracted from hair samples hundreds of years old. So maybe it'd be simpler to have a hair found?

I am not, however, an expert - we only had to cover a sort of basic course in Forensics for my law degree, so I'm pretty much just paraphrasing the textbook here. Hopefully one of the many experts on this board might be able to give you more useful and reliable information.

veinglory
10-19-2011, 07:04 PM
Is she buried just in the ground by the killer? In this case the DNA itself might be destroyed by bacterial action unless it is somehow protected. DNA that lasts is often encapsulated, such as the inside of a tooth. Of she is found and buried conventionally the problem with be more the cleaning of the body.

If you want the DNA to be preserved you might have it so she is wrapped in plastic or a tarp and buried somewhere cold.

areteus
10-19-2011, 07:52 PM
Certainly a few days, longer if the above conditions are followed. The main issue with this may be contamination of the sample with other DNA from soil - which is full of bacteria and plant tissue and other DNA containing stuff. Any foreign DNA in the sample will be amplified with the wanted DNA when the whole thing undergoes PCR and anything which casts doubt on the outcome is an issue (which is why forensics labs are so tightly regulated). From what I remember of carrying out PCR, even in a clean lab with a clean sample it is frighteningly easy to contaminate a sample and have that knacker your whole analysis.

mirandashell
10-19-2011, 08:06 PM
The thing is though, most readers will only know what they see on programmes like CSI. So if it sounds plausible, most readers will accept it. Even if it is complete tosh...... looking at you, Gill Grissom! With your images from victim's corneas!

Julie Reilly
10-19-2011, 08:12 PM
The current plan is that he is her headteacher, sees her waiting at a bus stop in the rain and offers her a lift home.

So her hair could be in his car simply from him giving her a lift.

But instead of taking her home, he takes her to a remote spot to have his wicked way with her. She struggles and scratches him. He strangles her to make her unconscious but goes too far and she dies.

He then leaves the body to go home and get a spade, coming back to bury her in the woodland. I could have him buying a spade in a local garden centre, then he'd be on CCTV if it was recent.

I was initially going to have this all take place several years ago, but it can be more recent. I really need to be able to have some sort of evidence linking him definitely to the body, not just circumstantial evidence that he could have picked up through being in close proximity to her innocently.

Zelenka
10-19-2011, 08:23 PM
The current plan is that he is her headteacher, sees her waiting at a bus stop in the rain and offers her a lift home.

So her hair could be in his car simply from him giving her a lift.

But instead of taking her home, he takes her to a remote spot to have his wicked way with her. She struggles and scratches him. He strangles her to make her unconscious but goes too far and she dies.

He then leaves the body to go home and get a spade, coming back to bury her in the woodland. I could have him buying a spade in a local garden centre, then he'd be on CCTV if it was recent.

I was initially going to have this all take place several years ago, but it can be more recent. I really need to be able to have some sort of evidence linking him definitely to the body, not just circumstantial evidence that he could have picked up through being in close proximity to her innocently.

Does the struggle take place in the car? As in, does he park up and then try to have it away with her? If so, and if she tries to defend herself in the car, you could have blood evidence from the struggle as well as her hairs maybe? She could also have dropped something during the struggle, something that could be traced back to her (like, if it is recentish, a cellphone or maybe a notebook or something, I dunno).

Also, what did he do with the spade afterwards? Could be he still has it, albeit hidden away somewhere, too frightened to dispose of it in case it's found?

Zelenka
10-19-2011, 08:25 PM
Oh, also, what does he strangle her with? Hands or some sort of ligature? If the latter, what happened to that? Was it left with the body? Is it something that could possibly be linked back to him or to her?

LynnKHollander
10-19-2011, 08:26 PM
... Even if it is complete tosh...... looking at you, Gill Grissom! With your images from victim's corneas!
Really? That's an old superstition.
Randall Garrett's Lord Darcy's forensic sorcerer -- I forget his name, Master Sean .... -- can do that, but with magic, and then it turned out to be so subjective as to be useless as evidence.

mirandashell
10-19-2011, 08:34 PM
From what I can remember, the CSI cornea thing was different. It was done from a still image of the victim.






..... I do love a pedant......








LOL!

Zelenka
10-19-2011, 08:40 PM
From what I can remember, the CSI cornea thing was different. It was done from a still image of the victim.


The Doctor did it too, with a dead Wirrrn.

mirandashell
10-19-2011, 08:54 PM
Well yeah, but that's Doctor Who. He can do anything.

A lot of people think the science in CSI is real.

Zelenka
10-19-2011, 09:06 PM
Well yeah, but that's Doctor Who. He can do anything.

A lot of people think the science in CSI is real.

I only watched CSI because my mum was into it. I found it hilarious from the outset. CSIs interviewing suspects for starters, and that's before we get to them wandering around crime scenes without so much as a face mask.

For the OP though, I was just thinking - if there was a struggle in the car, you could also have broken fingernails from the victim, or even torn pieces of clothing, buttons or something, that might match the clothes on the body. Something small that might have been missed when he cleaned the car up?

LynnKHollander
10-19-2011, 09:34 PM
I found the idea of all those lab rats wandering around armed frightening.

Becky Black
10-19-2011, 10:27 PM
There's hair and fibre. They were using matching hair to connect victim and killer long before DNA tests. The body will have picked up fibres from his clothing and his car when he was moving it around, and of course his clothing or his car will have picked up hair and fibres from her.

It's pretty hard to eliminate all blood traces from anything used to transport the body. Even if you can't see it any more there are still traces there. One drop of her blood in his car could convict him. And don't think there's no blood because he strangled her. She could end up with blood coming from her nose or mouth. He might not even see it if it's dark. It could only be a mist of blood coughed or exhaled by her.

It's amazing what will finger the killer in the end. I saw a true life crime show once where the police matched up the garbage bag used to wrap the dumped body of a baby the parents claimed had been abducted to a roll of unused garbage bags at the parents' house. They lined up the bags at the perforations and the patterns of colour irregularities in the plastic lined up perfectly.

Maybe you could take a look at news sites, look at crime stories and see what forensics they used to actually connect the killer and victim. There's definitely more than DNA to play with.

Julie Reilly
10-19-2011, 11:03 PM
I think I'm making it unnecessarily difficult for myself by wanting to keep the murder in the past. It would be far easier to have it happen recently, then there would be fresh evidence, and the police will be far more on the case than if it were several years in the past.

I was just thinking it would be more dramatic and spooky for the ghost to be a missing person from years ago.

Zelenka
10-19-2011, 11:19 PM
I think I'm making it unnecessarily difficult for myself by wanting to keep the murder in the past. It would be far easier to have it happen recently, then there would be fresh evidence, and the police will be far more on the case than if it were several years in the past.

I was just thinking it would be more dramatic and spooky for the ghost to be a missing person from years ago.

If you can get something like the Crime and Investigation Channel, they run regular documentaries on cold cases, or maybe you can find something on YouTube, but I don't think it's beyond feasibility to have the police solve and older murder. Remember you could also have other evidence as well as forensics, like witnesses placing him somewhere or holes in his story that can come out.