Scene of the Crime (10 page)

Once that has been determined, experts can, if necessary, determine from what positions the muzzle flash should have been visible and from what places the report should have been audible. Although in real life this is rarely useful, in fiction it may be possible to locate a potential witness, or impeach a lying one, based on what has been determined from these tests. (I spent the better part of two years off and on trying to get a lead on a shooting that occurred in an alley, despite the fact that I was in the alley when the killing took place and didn't know about it until it was reported.)

Oh, you want to know more about that one? Well, it was this way. We—my husband and I—were in a mortgage company that backed onto the alley, arranging for a home loan. The back door of the mortgage company was open, and all three of us—my husband and I, as well as the agent we were talking with—heard the shot. We all got up, rushed back to the door, looked out into the alley, saw no sign whatever of any trouble, decided we had heard a backfire, and went back to the discussion in progress. I found out an hour later that the owner of a somewhat disreputable pawnshop, which was located in the alley and which sold musical instruments and repaired shoes on the side, had been shot to death—almost certainly by the shot we all heard.

Despite a lengthy and careful crime-scene investigation and a painstaking job of investigation by detectives, no suspect was ever developed. I have a few hunches of my own, as do the others who worked on the case, but none of them ended up proving anything.

How Far Can You Shoot?

Be aware, both in real life and in fiction, that a weapon may be able to fire farther than the person can see. Even a little .22 long rifle bullet (despite its name, it's as often used in pistols as in rifles) may travel as far as a mile, so that a person "popping cans" on a back fence in even a sparsely populated area may kill a person inside a house two blocks away. In November 1991, while I was working on this book, two young men got themselves into serious trouble on the Wasatch Front in Utah by setting up a firing range in their above-ground basement. When they began shooting at their targets with their .22s, their bullets passed out their wall and into the wall of the adjacent house, doing considerable damage. Fortunately, no one was seriously hurt, and the firing range was quickly discontinued.

In fiction as in real life, this carrying power means that the search for a slug—or the search for the place from which a weapon was fired, if it is known where the slug wound up—may occupy quite a large area.

Collecting and Using the Brass

In the case of an automatic or semiautomatic weapon, empty shells—usually referred to by police as
brass—
are ejected, and can be located unless the perp takes them away. Once located, the shells can be matched to the weapon (once the weapon has been located) by the firing pin mark on the shell and the ejector mark on the shell. Once again, photographing and triangulating are very important, as once the weapon is located, test firings that demonstrate how far, and in what direction, empties are ejected may—like triangulation of where the slug wound up—determine exactly where the person who fired the weapon was standing.

The empties should be collected very carefully. Albeit rarely, it has happened that a sufficiently large fragment of fingerprint for identification has been found on an ejected shell.

Ammo at the Scene

When searching a crime scene in which the perp probably lived in the house or in which the perp may have grabbed a weapon that was already in the house, it is critical to locate and collect every

source of ammunition in that house, so that shells can, if possible, be matched to the source.

The Expert In-and Out of-the Lab

What can be determined, and by whom, about guns and ammunition?

• Firearms experts can usually—depending on the condition of the slug—determine what make, model and caliber of weapon fired any given slug.

• Firearms experts can usually—again depending on the condition of the slug—determine whether a suspect weapon fired any given slug.

• Firearms experts
cannot
usually determine which shotgun fired which load of shot.

• Almost always—except in the rare instances in which a shell has been reloaded and refired several times—firearms examiners can determine which weapon fired which empty shell. This refers to handguns, rifles and shotguns.

• Using a gunpowder residue test, forensic chemists can usually determine whether or not a given person fired a gun within the last few hours, provided the test is used quickly enough.

Firearm and Trace Metal Residue Tests

However, the old paraffin test, which was extremely inaccurate, has been totally discredited. Its technique of coating the hands with warm (not hot) molten paraffin, letting the paraffin harden, then stripping it off and checking it chemically for nitrates (the most common chemicals released when a gun is fired) not only gave false negatives when an insufficient quantity of gunpowder residue was present, it also gave false positives if the suspect had been working with fertilizer or even changing a baby's diaper.

The best test is a neutron activation analysis (NAA), but this test is so expensive that it is not always used. The test is done on swabs dipped in a 5 percent solution of nitric acid and wiped over the suspect's hands in a given order with particular concentration on the palms of the hands and the webbing between the thumb and first finger, where gunpowder residue tends to collect in the creases. The NAA tests for the less-common barium and antimony contained in gunpowder. Fortunately, the same chemicals and techniques used in the field for the NAA are also used for less expensive chemical tests, so the investigator does not have to decide at once which is to be used.

However, the better the weapon, the less powder it is likely to discharge onto the shooter's hands. A really well constructed weapon may produce a negative residue test unless an actual NAA is used, rather than its chemical stand-in; a Saturday night special may discharge so much powder that "powder tattooing" may be visible for several days on the webbing between the forefinger and the thumb. (It may also begin to shave lead after it's been fired several times. "Shaving lead" means that the barrel is so far out of line with the cylinder that although most of the slug goes out the barrel, a thin sliver of it is propelled backwards toward the shooter's hand. This happened to me once, when I was test-firing a cheap .22 pistol. The lead shaving produced a cut and the gunpowder got in the cut. I do not recommend this for fun.)

A trace metal test used quickly enough can almost always determine whether a particular person has
held
a firearm in the last twenty-four hours. This is a field test: the technician sprays a chemical from an aerosol can onto the suspect's hands and then examines the hands under black (ultraviolet) light. The hands then glow different colors according to what types, and shapes, of metals the person has handled recently. The test works because handling any metal results in the transfer of submicroscopic molecules of metal from the object to the person's hands, and the chemical is able to detect these molecules. In test situations, it has been possible to see the horse-head insignia from a Colt revolver on the hands of the person who held the revolver.

If both trace metal and gunpowder residue tests are to be performed, the trace metal test must be done first, as the nitric acid solution removes the metal molecules on which the trace metal test depends. Also, although a lot of soap and water may on occasion remove the gunpowder residue, they usually do not remove the metal molecules the trace metal detects. This means that in fiction you can do a lot with using only one test, or with using them in the wrong order, or with letting the suspect wash his hands thoroughly before running any tests.

In Real Life: A Murder That Wasn't

And here's how it once worked in real life.

Detective Johnny Patton went to a killing. It looked like a murder. The dead woman was sprawled in the middle of the floor; women almost always lie down to commit suicide. There was no suicide note; women almost always leave one. The wound, although very close range, was not contact. The pistol that had apparently killed her lay several feet away from her. The wound went in a slightly downward direction, as if she had been shot by someone taller than she was. She and her boyfriend had been involved in a crime, and they knew that they were facing arrest. The roof, in effect, had caved in on them.

Neighbors had heard the two quarreling loudly. Neighbors had seen the boyfriend leave suddenly. Nobody had heard the gunshot.

The boyfriend was the obvious suspect.

But for some reason he told me he couldn't define, the case didn't "smell" right to Johnny. There was no ident officer on duty. Johnny called me to come in.

I did a trace metal on the boyfriend's hands. He had not held a weapon.

I did a trace metal on the victim's hands. She had held a pistol, in normal suicide position.

I did gunpowder residues on both, and Johnny suspended the investigation until the results came back from the lab.

The victim had fired a pistol. The boyfriend had not.

As we reconstructed the crime, the victim had held the pistol at arm's length and slightly up to fire into her chest, letting the recoil throw the pistol away from her, simultaneously committing suicide and framing her boyfriend for her murder.

Was the frame job deliberate?

There was no proving it, of course, but Johnny and I always thought it was. And if Johnny hadn't been experienced enough, and good enough, to sense that something was wrong and call me in, the boyfriend might have been convicted. The evidence against him was strong enough that a negative firearms residue and trace metal on him might not have meant anything, if we hadn't also had a positive firearms residue and trace metal on the victim.

You may have the case if you want it... but I already sold a short story using the forensic part and the legal part, but not the human part, of the case.

TABLE 3
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Some Characteristics of Handguns

• Automatic pistol:
may be set for single shot usage, or may be set to go on firing as long as the trigger is depressed and ammunition remains in the magazine; each shot discharges a round of ammunition, ejects the empty, pulls another round into firing position, and—if it is set for full automatic, the trigger remains depressed, and ammunition remains in the magazine—fires again. When it is set for single shot usage, it works like a semiautomatic (see below).

It is loaded by inserting a magazine, which may be loaded immediately before insertion or may have been loaded earlier. The number of shells in the magazine varies according to make and caliber; in combat situations, people usually carry extra loaded magazines.

An automatic pistol generally has a safety mechanism to prevent accidental discharge.

Examples: Beretta 9mm, Glock 9mm.

• Semiautomatic pistol:
frequently referred to as an automatic, although it is not a full automatic because it cannot be set for continuous fire. Before it is fired the first time, a slide must be pulled back to bring the first bullet into firing position. When it is fired, the empty brass is ejected and another shell is pushed into firing position, but the trigger must be released and rede-pressed before it fires again.

It loads with an insertable magazine, often called a
clip.
As in the case of an automatic, the magazine may be loaded immediately before insertion or earlier. The number of shells contained in a magazine varies according to make and caliber. The most common automatics have nine-shot clips, but some 9mm pistols on the street carry 30-round clips. In combat situations, people generally carry extra loaded clips.

A semiautomatic pistol generally has a safety mechanism to prevent accidental discharge.

Examples: U.S. Army Colt. 45, Browning .22 target pistol.

• Double-action revolver:
probably the most common handgun in civilian use today. It can be fired with a squeeze of the trigger; cocking is not necessary. Depressing the trigger automatically

pulls the hammer back into cock position and then releases the hammer, causing the weapon to fire. The cylinder then rotates to bring another shell into firing position. The empty brass remains in the cylinder until the cylinder is opened and cleared for reloading.

To load a revolver, it is necessary to open the cylinder, either by rotating it out to the side or by opening the gun on a hinge so that the cylinder and barrel fold forward from the grips and firing mechanism, providing access to the back of the cylinder. The number of shells contained in a cylinder varies according to make and caliber, but the most common revolvers have six-shot cylinders. Despite the invention of various fast-loading devices, it still takes considerably longer to empty the brass and load six shots into a revolver than it does to pop out an empty clip and snap a full one into a semiautomatic. This is one of the many reasons why police departments tend now to replace revolvers with automatics.

A revolver does not have a safety mechanism. The device on the side of the gun that some people mistake for a safety is in fact a cylinder-release device.