Forensics Questions

Thanks for filling us in.

HoratioStalker said:

I attended a talk with a real forensics person from the Hillsboro Police Department, and Dynamo is correct - they wear basically bunny suits and booties to not contaminate the scene. Not terribly fun for TV viewers! DNA results can sometimes take months or even years to come back, and they don't test every little thing because it is an expensive process, so unlike the show where they test every cigarette, every glass, that would not actually be done. Fingerprints are also manually evaluated first before being entered into the computer. The analyst selects the key points on the print he or she thinks are the identifying features of the print, and again, results are not instantaneous. You may have a 10-card on someone and a partial index finger print, but you don't know what finger you have, so the computer is running all 10 to compare, times however many people are in the database. TV shows you the art, but it really is more hard core science.

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DNA is hardly used in cases like burglary/robbery. One, because it takes too long and is too expensive - and you need something to compare it to otherwise it is useless; two, there is usually much better evidence at the scene like toolmarks/impressions and prints.

AFIS only became mainstream in the mid/late nineties, if memory serves. I know in the US a computer match is sufficient in court, but in the UK a print still has to be physically matched by an expert before it is admissable in court. Never see that in a tv show lol.

And yes, SOP is full noddy suit, booties and gloves at all times. Including the hoods, not hair nets. Not used for main characters because it covers their face/allergic to latex/uncomfortable/hampers sound pickup - don't remember which producer/show said that.

Mrs. Sanders said:

you're basically right

according to my teachers, the conditions of a crime scene (climate, illumination, etc) should not be altered... at least not without taking notes/pictures/videos first...

if the first personnel who arrives at the scene (police officers) have to alter something (for example, break the door to enter the scene) they must communicate it to the crime scene investigators.

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First thing an investigator does is grill the other people at the scene. Everything is documented. In the UK, written notes at the scene are evidence in themselves and have to be treated as such. As are photos. The first item of evidence is a scene sketch. All parameters are measured and recorded, then adjusted if necessary. Unless the evidence is in danger of being lost, it isn't disturbed until its been sketched, photographed and written in the notes. If it rains, you start doing a chicken dance and cover as much up as possible.

Specific procedures are probably universal, but I warn you I'm only really familiar with UK scene protocol. The science, however, is the same. I'm new to this thread, so I'm gonna start at the beginning and see if there's anything else I can add.

11krage said:

In a episode of csi during a game hodges 'died' from a prefired bullet that was matched via ballistics to a destroyed weapon. It was fired from a small doohicky that presumably (please correct me if I'm wrong) left no extra striation markings.

1. What exactly was the doohicky and how does it work?

2. Is there a way to make or use something that can fire a prefired bullet without adding extra striation markings or distorting the ones already there longer range, say the distance from the roof of one building to the window of another in new york. Or is this only possible at short range?

3. If a prefired bullet is slightly misshapen through previous impact will this affect its trajectory or impact affect?

Don't worry no criminal intent here, just curious.

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I don't recall the 'doohickey' but I can tell you a little bit:

The striations are left by rifling on the gun's barrel. Barrels are rifled to make the bullet rotate when fired to make it more accurate. A smooth bore barrel would not produce these marks (it would therefore be less accurate). Homemade weapons generally don't have rifling as the technical skill is quite high.

Firing a prefired bullet would depend, I would think, on whether you can make it viable with a cartridge. Something like an air rifle would be able to fire prefired rounds, provided they fit in the barrel still, without needing a cartridge.

The misshapen bullet would kind of depend on what it impacted with. A mushroomed bullet would be no good to man nor beast.

Out of interest, you could fill a rifle cartridge with pretty much anything as shot and it would do some damage. Solid cartridges are banned but a rifle cartridge is just high velocity shrapnel.

Hope that helped somebody

Bullit 01, thanks for your insight. Are you an investigator or do you know one?

Just one little thing, you can edit your previous post within 24 hours of making it. So in the future, do not double post, just add onto your first post if it is still within the time frame of editing it.

Trained as a crime scene manager in the UK. Sorry about the double post, my internet reset and I couldn't edit the first post again. My bad.

Oh no problem on the double posting. Just wanted you to know.

Very cool that we have someone here who is trained in the field. Your input is very welcome.

I was wondering if it's possible to get bone marrow from a femur, that belonged to the person who has been dead for two weeks, and still use that as a reliable source of information?

That's a good question Karlia.

I think it is... but I'm not so sure...

I'll see if I can find something

Bullit 01, great to know a real crime scene investigator... hope I can become one soon (I'm almost finishing a degree in forensic sciences)

and let me say the crime scene protocols are very similar around the world, you guys basically do the same things that we do here in Argentina (yeah, I live SO far away )

I looked for something...

according to this study, DNA extraction from the bone marrow is possible many years after the person's death...

and -quoting another book that I've found-

"the advantages of the bone marrow extracted from an intact femur is that contamination....

*we can add body decomposition here too*

...can be minimized or eliminated since the marrow is extracted from a "closed" organ...."

so, the answer to your question is definitely YES.

Interesting.

Just remember everyone, that you can edit your posts for up to 24 hours, so instead of double posting, just edit your previous if 24 hours has not past. Thanks!

I know... I know...

(In fact... I did it in the first post)

just wanted to separate things

Thank you

I used to be very interested in forensic anthropology and I just love bones and the information they can give. Geek!

Another question: can voice print tech be used to identify a suspect even if the voice has been electronically distorted? Is there any way to filter out the distortion?

What's the liquid used on the cotton swab?

The transparent water-like liquid used for extracting blood from a crime scene/body/fabric? I'm wondering. :O

Re: What's the liquid used on the cotton swab?

c.rising said:

The transparent water-like liquid used for extracting blood from a crime scene/body/fabric? I'm wondering. :O

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I'm going to move this over to the Forensics Forum where it might be more likely to get answered, but I'll leave a redirect in case anyone here knows the answer and wants to post.