Saturday, November 6, 2010

Regarding Gunshot Residue: Dont Forget the Plumbum

Time for another "news we hope you can't use" public service post. This one involves a modest amount of chemistry, so buckle up.

Frances Elaine Newton is dead today in large measure because the State of Texas claimed to have found a trace of nitrate on the hem of her skirt. To the people of Texas, at least to those twelve Texans sitting in judgment of her, nitrates equaled gunshot residue. They had no choice but to convict her of capital murder.

Here's a picture of a handgun firing a bullet. The picture is from my "don't go anywhere without it" copy of Gunshot Wounds. (If you have $120 laying around and want to browse through 424 pages of gruesome pictures, you could do worse than get yourself a copy. I used the book extensively when working on The Trial of Bryon Case.) You can see  the guy's hand will soon be covered in gunshot residue. It's likely, but not certain, that the long sleeve of his sweater will also be contaminated. It's extremely unlikely, however, he will end up with any detectable gunshot residue on the hem of his full length kilt.

Most of the smoke you see is potassium nitrate, also known as saltpeter. Potassium nitrate is a primary ingredient in gunpowder. Each saltpeter molecule consists of a potassium atom (K, from the Latin word kalium) and a nitrate molecule NO3. The nitrate molecule in turn consists of one nitrogen atom (N) and three oxygen atoms (O3). The smoke you see in the picture consists largely of KNO3 molecules.

When law enforcement agencies test for nitrates, they are frequently testing for the presence of the nitrate molecule NO3. If they find NO3, and if they really want to convict someone based on that finding, they simply pretend they found KNO3 when all they really did was find was find NO3. They then cross their fingers and hope the jurors will not be readers of this august blog.

One problem with the nitrate test, and it is a major problem, is that lots of things have NO3 floating around inside them. If you've applied cosmetics, there's a chance you applied a little NO3. Nitrates of various forms are used in toners, astringents, moisturizers, cleansers, acne treatments, hair colorings, and fingernail polishes.

If you've had one of the world's best pastrami sandwiches from Langer's, you could have dripped some NO3 on yourself. Nitrates are used in cured foods, bacon, hot dogs, deli meats, smoked fish, and beer. They are also found naturally in vegetables.

If you have smoked or been around a smoker, good luck. Tobacco contains NO3, as do car interiors, pharmaceuticals and some drinking water.

That's not the only problem with the nitrate test. The test also will also sometimes claim to have found nitrates when it really didn't. Sometimes it will have only found dichromate (for those of you working in a chrome plating factory), or hypochlorite (for those of you who use chlorine bleach), or selenium oxide (for those of you who shampoo with extra strength Head and Shoulders.)

In the case of France Elaine Newton, now deceased, the state of Texas probably discovered fertilizer rather than gunshot residue. Potassium nitrate is one of the primary components of fertilizer. It provides both potassium and nitrogen, as you might infer by its chemical symbol KNO3.

One of the victims of the shooting, 21-month-old Farrah Newton, had spent the day at her uncle's house. The uncle kept a large garden in his back yard, and Farrah was reportedly exposed to the fertilizer. It is entirely possible, and it makes more considerably more sense, that the nitrate found on the hem of Frances Newton's skirt was transferred there inadvertently by young Farrah not long before she was murdered.

There is, of course, a way to distinguish between gunpowder nitrates and fertilizer nitrates, but the people of Texas didn't go to that trouble. If they had taken the trouble, they would have noted that gunshot residue will also contain some combination of antimony (Sb, from the Latin stibium), barium (Ba), and lead (Pb, from the Latin plumbum). If you look closely at the picture, you can almost see the plumbum atoms.

You generally won't be finding a similar combination of Sb, Ba, and Pb in fertilizer.

In an effort to save Frances' life, her appellate attorneys tried to get the skirt tested more thoroughly, to determine whether there was some combination of stibium, barium, and plumbum on the skirt to go along with the nitrate. Given that the people of Texas hadn't done the testing before condemning Frances to the gurney, it seemed like a reasonable request. Unfortunately, Texas used destructive testing (unnecessarily, of course) when they initially tested the hem for nitrates, so there was no nitrate-stained hem left to be tested. That was fatally unfortunate for Frances.

Now you get to ask yourself. If you are sitting on a jury, and the State asks you to convict someone because they had nitrate on the hem of their skirt or kilt, will that be sufficient for you to vote guilty? Or would you demand the state provide more substantial proof?

Your choice.

Your constitutional obligation.

No comments:

Post a Comment