Friday, May 28, 2010

The Ballistics Expert in Criminal Defense

Ballistics has been on my mind these past few weeks. I'm defending a criminal murder case in Brazos County which relies heavily upon the prosecutor's ability to link my client to the alleged murder weapon with the expert testimony of a firearms examiner, or ballistics expert.

The criminal defense attorney defending such prosecutions needs a fundamental understanding of the firearms examiner's role in presenting evidence concerning the identification of firearms and ammunition. This is especially true in cases where such identifications are the lynchpin of the prosecution or defense case. Understanding how bullets and cartridge cases can be identified as having come from a specific weapon depends on some knowledge of how firearms are manufactured, particularly pistols and rifle barrels.

First, a hole is bored through a cylindrical bar of steel of the desired diameter. That diameter determines the caliber of the weapon. Next, after the hole is bored, twisting grooves (or rifling) are created inside the barrel. This process causes a fired bullet to spin as it leaves the barrel, giving it more rotational velocity and, consequently, more stability with better accuracy. Regardless of the manufacturing process, each barrel acquires minute marks, called striations (or striae) through minor accidental occurrences in the rifling process. These striations are supposedly not the same for any two barrels and are the basis for the "individuality" of each rifle barrel. Any bullet fired through the barrel will be effected by the unique rifling of that particular weapon.

If a bullet (or bullet fragment) is obtained during the police investigation, often the police want to determine whether a particular weapon fired it. Assuming the police also possess the suspected weapon, the process of identification is straight forward. First, the examiner fires a series of test bullets from the suspected weapon and uses them to compare with the "unknown" bullet obtained during the investigation. The examiner uses a binocular comparison microscope, which is an instrument consisting of two separate microscopes mounted side-by-side. The unknown bullet is placed under one microscope and the test bullet under the other. The examiner then scrutinizes both bullets and attempts to locate similar striations that "match" both the test and unknown bullets. In theory, a careful study of all the detail on both bullets permits the examiner to conclude whether both bullets were, or were not, fired through the same barrel.

In a later post, we'll discuss the identification of a cartridge case and whether is was fired from a particular weapon. Although different from bullet identification, the same principles of probability apply.

8 comments:

Anonymous said...

Is your client facing the death penalty?

What draws the line on sentencing?

Stephen Gustitis said...

My client is charged with "straight" murder, as opposed to capital murder (a death penalty case). For murder a person faces 5-99/life in Texas prison. The judge, or jury, depending upon the defendant's choice, would decide the punishment. Thanks for writing in.

Anonymous said...

I have always wondered how the process of ballistics work without a gun being present? If you have no eyewitnesses, evidence, or dna can a client be charged with the crime? There are many charges brought against innocent defendants, so I'm curious about the phrase "beyond reasonable doubt." I'm a relative of a murdered victim and I want closure, but not "beyond reasonable doubt closure." I think every defendant deserves a fair and logical trial.

Stephen Gustitis said...

Thanks so much for writing. Typically, ballistics evidence is circumstantial evidence that links a weapon to either a particular suspect, or to a crime scene, or both. If a suspect is in possession of a weapon linked to a crime via ballistics, then the suspect "has some explaining to do." There will probably need to be some additional evidence to prove guilt, but of course, every case is different in that respect. Beyond a reasonable doubt (BRD) is the burden of proof placed upon the State in a criminal trial. Ballistics evidence might help a jury decided, BRD, that a suspect committed the crime. Or it might not, again depending upon the case. I hope this helps.

Anonymous said...

After reviewing your website and seeing how you interact with the public, I think having you as a defense lawyer would be great. I have two more semesters to finish my paralegal studies degree. Most colleges in my area have lawyers as the instructors. Your website is very educational and helpful. Thanks for the response. You seem like the type of lawyer who "cuts the BS." I hope to attend a trial in Texas this coming October 19. I have faith that the truth will be told. The LAWS of the BIBLE say that God loves Justice. Again I think you are a very intelligent and determined attorney. A little saying for the defense: "Just because they point the finger at you, doesn't mean you're the one to blame."

Stephen Gustitis said...

Thank you for your kind words. Good luck with your legal career.

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