I was watching a movie and after being shot a criminal sprayed the blood with ammonia to keep the detectives from using his blood for a dna sample. Was this hollywood fiction? I didn't think ammonia would destroy blood dna samples...

I've heard that a topical solution of hydrogen peroxide will destroy DNA,

I've also heard that bleach will do the job.

I've heard that a topical solution of hydrogen peroxide will destroy DNA,

I've also heard that bleach will do the job.


Huh. I figured it was hollywood hype. I wonder why all criminals don't carry around bleach, hydrogen peroxide, or ammonia. Anyone know if this is fact or fiction?

It might not necessairly destroy the DNA as much as it would contaminate the sample and make it unusable in the chemical reactions needed for anlysis (PCR?)

DNA is a relativly fragile chemical. Hydrogen peroxide would probably destroy it, if it was concentrated enough. A sodium hydroxide solution would certainly work.

Was the movie "the Boondock Saints"?

Mature human red blood cells do not have nucleii, and therefore no DNA. From a bloodsplatter, the amount of available DNA would be locked up in phages and tissues that got torn loose.
While complete and utter destruction of DNA would be rather difficult to perform (especially in a shootout), you could use a PCR inhibitor, (though I'm uncertain of using straight ammonia, NH3). BY inhibiting PCR, you could make it extremely difficult to replicate DNA.
PCR stand for polyermerase chain reaction, which basiacally amplifies DNA, or replicates it a gazillion times.
I run lots of PCRs, and one of the chemicals we use as an inhibitor is BSA, or benzyl sulfonamide. BSA contains an ammonia group in it, and too much BSA will prevent the PCR.

So it is entirely plausible that NH3 would goof up a CSI's attempted PCR, especially if the NH3 concentration was high enough.
There are methods that you can use though to extract DNA, or remove PCR inhibitors, so by using ammonia you would only slow down the cops' investigation.

Despite what Nasor says, DNA is a surprisingly robust chemical. If you were to damage the DNA, which would be easy, you could prevent entire genomic sequencing. However, the type of genetic analysis that CSI does is on very small, well known regions of DNA, so partially fragmented DNA may not be a problem.

Sodium hydroxide would screw over CSI's efforts.

Mature human red blood cells do not have nucleii, and therefore no DNA. From a bloodsplatter, the amount of available DNA would be locked up in phages and tissues that got torn loose.

Ever heard of white blood cells? :)

You most definately can get DNA from blood samples.

But I don’t have the knowledge to definatively answer the original question. Bleach (ie. dilute sodium hypochlorite) will degrade DNA and greatly reduce the likelihood that it can be used for biological analysis, such as PCR. It will also degrade proteins and most likely prevent immunological detection of blood group antigens. But when it comes to merely detecting the presence of blood, there are some very sensitive fluorescent dyes that can detect even minute traces of blood, even after it has been cleaned and scrubbed away from visible sight. Bleach will react with DNA but it won’t degrade it down to individual nucleotides. It really takes a lot of chemicals and a lot of ‘elbow grease’ to beat forensic DNA dyes.<P>

Yeah, it was Boondock Saints. Most of the responses are a little above me.

I don't know what sodium hypochlorite is, or NH3, or Sodium hydroxide. Interesting though.

NH3 is ammonia. It is a nitrogen atom with three hydrogens attached to it. Sodium hypochlorite is bleach (in a dilute form, as Hercules Rockefeller stated). There is an oxygen bonded to a chlorine, but since only one of oxygen's two binding sites is filled, the oxygen carries an extra pair of electrons and has a negative charge. The sodium has a positive charge and interacts ionically with the hypochlorite.

NaOH is sodium (Na) hydroxide (OH). It is a very strong base (opposite end of pH scale to an acid, with similar effects in that they both can be very destructive).

Hope that clears some things up. Ask more questions if there is still more you don't understand. After all, we're all here to learn.

Boondock Saints was a great movie, by the way.

boondock saints was sweet movie

How long does traces of DNA last in a crime scene?

After how long can blood still be detected, even after it has been wiped away from human sight?

Thanks! That does clear some things up Idle Mind. These forums are pretty d*mned interesting.

DAMNIT!!
Too late.

Oh well- interesting question:
After how long can blood still be detected, even after it has been wiped away from human sight?
Years and years.

Trying not to get exited here (murder, favorite subject), but forensic cases have been known to remain cold for up to 30 years and then solved by blood evidence still at that scene

The question of what would destroy DNA has already been more or less answered, but now where the simple detection of blood is concerned.
There is a chemical sprayed on any suspect area called luminol
http://people.howstuffworks.com/luminol1.htm

its a compound made primarily of carbon and hydrogen with nitrogen in the formula (which you can tie in to this legend of spraying ammonia)- and they mix this with hydrogen peroxide which would further destroy DNA; either way, DNA is a very fragile molecule.

However, DNA or not, this compound binds the heme group in hemoglobbin( more like the iron atoms in that protein) found in blood cells so it wouldn’t matter one way or the other if DNA were present or not.

So you spray it on, let it set, and turn the lights out. Everywhere that blood was present- even if it was wiped out by strong chemiclas such as bleach or ammonia- would show up as fluorescent streaks glowing in the dark.
Which is eery.

I've seen crime scenes where you can literally see how and where the killer wiped off blood, just by looking at each glowing area you can imagine the sponge in his hand as he wiped.
And you could also, 30 whole years later, trace where the body was dragged by the glowing strip on the floor.

However, DNA or not, this compound binds the heme group in hemoglobbin( more like the iron atoms in that protein) found in blood cells so it wouldn’t matter one way or the other if DNA were present or not.That's very interesting. What if you treated the blood with something to strip the iron center out of the heme group, like EDTA with sulferic acid or some other strong chelator?

Nasor:
That's very interesting
Isn't it??!!
Muhahahhahaahah.

Then again not- science is making it very hard for clever murder.
Count your stars I can use this as an excuse for not killing your family.
~kidding~

What if you treated the blood with something to strip the iron center out of the heme group, like EDTA with sulferic acid or some other strong chelator?
From my understanding of this, the iron’s main use its its ability to catalyse the fluorescence.

This means that without it, you could still be able to detect blood there but only with more complicated tests- iron just makes this easier by making the detection visible to the naked eye.

Even so, as wonderful as this sounds it has its own problems- detergents and even bleach can make luminol glow so that there are cases where this chemical is sprayed (say a laundry room, and I've seen it happen) where blood was never present, putting the innocent under suspicion.

So the use of EDTA or sulfuric acids can do one of two things:

1. Destroy the iron atoms in the protein, which would render the sample undetectable in the dark
2. Or actually enhance the glow, the way some detergents do

Either way, you'd still be able to detect if blood had been there if it had.

Sprays like this can also be used to detect saliva and semen- so if you think you'll get away with it 'cause ya strangled the bitch, hence no blood, think again.

about there blood dectecting dyes. Wouldnt sodium hydroxide DESTROY not only the blood but basically (unless it was glass or stainless steel) most of the substance the blood is on? We use it at work to clean grills and it eats ANYTHING, your left with the shiny steel underneath no matter how much crap was on the grill

Wouldnt sodium hydroxide DESTROY not only the blood but basically (unless it was glass or stainless steel) most of the substance the blood is on? We use it at work to clean grills and it eats ANYTHING, your left with the shiny steel underneath no matter how much crap was on the grill
Pause.

Then what would be the point of checking?
That's like trying to palm a fingerprint off an amputee.

This is for surfaces that appear clean to the nake eye- carpets, floors, tables- that most people wipe off with simple bleach or soap.

that was kind of my point. Yea it would get all the blood but the cops would know SOMETHING had been going on due to the half gone floor and furniture:p

but out of interest say you kill someone over a sink (stainless steel) and all the blood goes into the sink then you could destroy it with grill cleaner because it would clean it all up

but out of interest say you kill someone over a sink (stainless steel) and all the blood goes into the sink then you could destroy it with grill cleaner because it would clean it all up
Easier said than done, Assman.

Blood spatter.
You can't bash a skull in without blood exploding out everyfuckingwhere- yes, I know, 'Duh'.

You'd have to kill a person in a bag to not leave any trace evidence, period.

(They can not only detect the teeniest hints of blood but by reading the shapes of each drop they can tell how you killed, what you used, and where you were standing when you did it.)

And if you're going to kill them in a bag then what's the point of klling them "over the sink", stainless steel or not?

Do what us women do- POISON.
But even then, they'll read the hair and pinpoint exactly what you posioned them with and for how long. They can actually make a calender out of a corpses hair (usually with arsenic).
You can't kill anyone anymore.

FUCK SCIENCE.

At any rate-

"Yea it would get all the blood but the cops would know SOMETHING had been going on due to the half gone floor and furniture"

I think Nasor was talking about a simpl compound that could wipe out the iron, not eat through the floor or carpet.

The detection of blood evidence (with Luminol) is one thing,
the deciphering of DNA is another.

People, lets use the tried and tested method.

Make it look like an accident.

Or frame someone else.

Have a good alibi.

maxzuk:
The detection of blood evidence (with Luminol) is one thing,
the deciphering of DNA is another.
Bing-o.
Make it look like an accident.

Or frame someone else.

Have a good alibi.

..and become a cliche.
Like the one about "my wife accidently fell down stairs, shot herself, stepped off canyon."
My child "accidently fell down stairs, chocked on milk, stepped off canyon with the wife"

My parents both committed suicide.

Perfect alibi or not, you will always be destroyed by Motive.
The second they find an insurance policy or that you were in any way compromised by the person (specifically if they're either a spouse or close relative)- slam. You're a suspect.

The perfect murder, therefore, would be one where you can erase every last stitch of evidence, down to the atoms.
And the victim is a complete stranger to you.

Which sounds almost impossible.
Unless you get an itch to kill a random baby by shoving it on railorad tracks.

I'd like to correct myself.
BSA is actually Bovine Serum Albumin, not benzyl sulfonamide.
Urea, which naturally decomposes to ammonia, is present in urine, and from urine you may extract DNA. All you need are the right organic solvents and clean up kit, and you can isolate the DNA.

Ever heard of white blood cells?
Of course. Notice that I said tissue and phages. As in phagocytes. As in white blood cells.

Some blood hemes are very potent polymerase inhibitors, incidentally.

Gendanken,
You can't kill anyone anymore.
I disagree. If you wish to kill for the sake of killing, not for the sake of removing a person you don't like, it'd be really easy to get away with.
Just kill someone no one would care about.

[edit]
Right, unless you like shoving babys on railroad tracks.

Of course. Notice that I said tissue and phages. As in phagocytes. As in white blood cells.

Oh, I see. :eek: I've never seen phagocytes referred to as "phages" before. (But I'm no immunologist, that's for sure.) To me the word "phage" means a bacterial virus, so you can see why I thought it was odd that you were citing 'phages' as a source of DNA in blood! :) <P>

Yeah, that was definitely my bad with terminology there.
I was refering to the Latin roots, though, where phage means an eater or destroyer. Bacteriophage= virus that destroys viruses, phagocyte= a cell that eats other cells.
Sorry for the confusion.

I disagree. If you wish to kill for the sake of killing, not for the sake of removing a person you don't like, it'd be really easy to get away with.
Just kill someone no one would care about.

Allready covered.

The best killers are those that kill as in eating. The worst are the idiots that make it an abstract, like BTK.

MORON.
Son of Sam.
MORON.
Every last one on this forum, including myself, fall in this category.

This goes mildly off the direct topic but I was wondering how well Coke works to get rid of blood evidence. I've heard stories about criminals stabbing knives into two liters of coke and leaving it to clean away the blood. Does this really work? I assume that since Phosphoric Acid is an active ingredient in Coke that it would dissolve just about anything over time, but does it do it well enough that no traces of blood are left at all? My mind says yes, but at the same time you'd think that the knife would dissolve a bit too.

AMansamoeba (nice handle)
This goes mildly off the direct topic but I was wondering how well Coke works to get rid of blood evidence. I've heard stories about criminals stabbing knives into two liters of coke and leaving it to clean away the blood. Does this really work? I assume that since Phosphoric Acid is an active ingredient in Coke that it would dissolve just about anything over time, but does it do it well enough that no traces of blood are left at all? My mind says yes, but at the same time you'd think that the knife would dissolve a bit too.
Intersting point, never thought of it.

But those criminals are wasting their time.
According to Snopes:

http://www.snopes.com/cokelore/acid.asp


The percentage of phosphoric acid in Coke is not even a percentage of the formula (its a .20-.30 percent RIP-OFF).

So rub all you want, you’re not really doing anything other than perpetuating an urban myth about Coke and smearing whatever you’re trying to destroy with glucose.

Interesting also, as far as acids go you’re more likely to be damaging your teeth from drinking orange juice than you are coke as it has higher concentrations of citric acid.
So I’ll remember to laugh next time at my Self Rigtheous Prick of A Dentist when he tortures me with the horrors of drinking coke- he’s got teeth as yellow as the orange juice he ate with his tofu that morning.

And the ingredients in coke cannot dissolve metal.
That too is an urban myth.

True that. I put a penny in a glass of coke for weeks, and it came out shiny as ever. The dental danger of coke comes from the high sugar content (which, these days, is at least that of most juices).

Can't resist:
"I put a penny in a glass of coke for weeks, and it came out shiny as ever"

I've put a hundred up my ass, and put two of them up as Ass (http://www.uprightcitizens.org/08/detector.html) Penny Threads.
Fun, fun..

"The dental danger of coke comes from the high sugar content "

If only.
America has thehighest obesity rates in the world.

and two corrections before I exit this dead thread:
So rub all you want, you’re not really doing anything other than perpetuating an urban myth about Coke and smearing whatever you’re trying to destroy with glucose.

Fructose, not glucose.
he’s got teeth as yellow as the orange juice he ate with his tofu that morning.
Drank, not ate.

Ta-ta.

gendanken, how about HF for killing someone? As an acid, it is very weak and doesn't even chew away viciously at your skin. However, the "symptoms of skin exposure to dilute HF are not felt immediately, but exposure of less than 10% of the body to it can be fatal, even with immediate medical treatment" (Wikipedia). Basically, you'll feel a burn but later your bones will start to decompose, which I understand is VERY painful. Hydrofluoric acid can be circulated through your body too, so if you're lucky then you'll only have to have a few limbs amputated (depending on dosage).

Sooo... spray someone with some of this and see what CSI thinks about it... Course this is just for killing, not covering up a kill---just thought I'd add to the discussion. There are bacteria too which are just as effective... Something the KGB use(d) and you don't need more than a pin prick to deliver death. I think I read in a newspaper of a Russian politician feeling a slight sting of a needle (turned out to be the point on an umbrella) while getting off a bus, a large lump on his leg the next day, and a large tombstone on his head the next (may have been 2 or 3 days actually..). Anyone heard anything like this though?

DNAse destroys DNA.

I was watching a movie and after being shot a criminal sprayed the blood with ammonia to keep the detectives from using his blood for a dna sample. Was this hollywood fiction? I didn't think ammonia would destroy blood dna samples...

ApOpTosis.
When that baby is born a small gun in every cell cuts the telemers out so that when that bullet strikes the heart...the last breath will be reminding of that predestined death in this young innocent world.

As my highschool chem teacher explained to us, it's much easier to get rid of a body with a bathtub of a very strong base - soak the body in the base long enough and the body tissues basically turn into soap, which will easily wash down the drain. Then use a high-concentration hydrochloric acid to get rid of the teeth and hair, and you're good.

Woman!

excuse me for my ignorance but wouldnt all you need to do is break the hydrogen bonds holding the template and coding strands together thus making them unuseable for testing?

Interesting is the fact that the most effect solution to DNA profiles is contamination not destructions.

Many modern organized crime networks now have access to gene replication technologies. In the same labs that create the wondrous modern addictive drugs, they can produce sprays laced with unsuspecting individuals replicated dna. All you need is a hair, skin or salver sample, of the patsy, and you can produce buckets of DNA spray that you then spray liberally around your crime scene. Contamination is the bane of DNA criminal investigations, with a little money you can make anyone the offender..

Yes I have heard that bleach will destroy DNA but how could a perp be sure he got it all.

I was watching a movie and after being shot a criminal sprayed the blood with ammonia to keep the detectives from using his blood for a dna sample. Was this hollywood fiction? I didn't think ammonia would destroy blood dna samples... A very strong base could neautralize DNA and give off salt and water. Radiation also has some effects.

A very strong base could neautralize DNA and give off salt and water. Radiation also has some effects.

Why would it give off salt and water? Are you saying that this is a byproduct of a reaction with DNA? I don't know.

DNAse destroys DNA.

Kinda cool, although expensive. Hmmm where to get a Eppendorf cup large enough to place a body.

DNAase and RNAase

DNA destroys itself during the copy process
http://faculty.plattsburgh.edu/donald.slish/figures/Telo2.gif

Well, it doesn't. ;P

In addition, RNase, as the name already suggests, does not degrade DNA...

Indeed. When I make an RNA probe I add RNAse free DNAse to get rid of the DNA and keep the RNA.

RNAse is highly specific for RNA. DNAse is specific for DNA.

Sorry. I was just thinking they're both produced by the pancreas to breakdown nucleic acids. I don't know enough.