.RU

Chapter XIII: Toolmarks, Firearms, and Bullet Lead Comparison - Criminal Adjudication: The Challenges of Forensic...

Chapter XIII: Toolmarks, Firearms, and Bullet Lead Comparison

A. Toolmarks and Firearms


Toolmarks are the impressions left when a hard tool contacts a softer object. The marks may be generated during the manufacturing process, such as when the barrel of a gun is rifled by cutting tools which leave marks on the barrel. The marks may also be generated when a manufactured item, perhaps a tool itself, is used in contact with other substances, such as when a screwdriver or crowbar is used to break into a door or window. In turn, the use of the item generates further marks on surfaces of the tool itself that were not present at the time of manufacture, such as when a gun is repeatedly fired or a screwdriver is used over time on various other items.

When a suspect tool is recovered, examiners look for distinctive features, often microscopically. They seek first to identify "class characteristics," or features that are shared by many similar objects.343 Then they examine the item microscopically for "individual characteristics," markings which are thought to be unique to the individual tool or firearm.344 They may also classify some features as "subclass characteristics" when they are common only to a small group of the manufactured items.345 The analysis then is the comparison of two sets of marks to see if they can be identified by common individual characteristics.

Figure . Comparison of screwdriver (left) and punctured steering column



The proffered basis for expert toolmark testimony is that each set of markings is somehow unique.346 Such testimony has been almost universally accepted.347 Testimony about a variety of tools has been admitted,348 including screwdrivers and crowbars,349 bolt cutters,350 hammers,351 pliers,352 and a punch tool.353 Testimony about knives has been admitted when used as a tool.354 A Florida Court did, however, refuse to admit toolmark testimony about a knife when used as a weapon, finding no scientific basis for proffered testimony relating a particular knife to marks made on human cartilage.355

In this multitude of cases, the admissibility of testimony of toolmark witnesses seems almost presumed. However, in United States v. Green, the judge allowed toolmark evidence but commented that "[t]he more courts admit this type of toolmark evidence without requiring documentation, proficiency testing, or evidence of reliability, the more sloppy practices will endure; we should require more."356

Weapons used in the commission of crimes are a prime source of evidence, as investigators seek to identify a particular gun as the unique source of bullets or other ammunition components. Firearms testimony is simply one branch of the larger field of toolmark evidence. As with some other types of toolmarks, firearms examiners assert that marks on firearms and ammunition bear individual characteristics that are particular to one firearm and that can be reproduced only with that firearm. The marks made by tools in the manufacture of guns or ammunition may result in particular corresponding marks on bullets, cartridge cases, and shot shells as they process through the firing mechanism.357

Manufacturers cut a groove in the barrel of a gun so that the bullet spins as it travels through the barrel to make it travel straighter when it leaves the barrel. This "rifling" process leaves marks and scrapes on the barrel metal. When a bullet is fired and travels through the barrel, the barrel marks are transferred to and reflected in marks, called "stria," on the fired bullet.358 As the gun is used repeatedly and as the barrel is cleaned, the marks in the barrel, and the resulting stria on the bullet, may develop more individual characteristics.

Other individual gun characteristics can be imparted to the brass cartridge case of the bullets as they are fired and as they are ejected from some types of guns. As the firing pin strikes the cartridge, it leaves its mark. As the cartridge case is blown back to the breech of the gun, the toolmarks in that area of the gun are impressed on the exterior of the casing. If the gun ejects the casing, the toolmarks of the extractor and ejector parts of the gun are imparted to the exterior of the casing as well.

To compare bullet striations or cartridge impressions, a recovered gun may be test fired so that the test bullet or casing can be compared to a found bullet or casing to see if they originated from the tested gun. As with other toolmarks, a firearms examiner makes initial visual determinations of class characteristics. The markings are then compared with a comparison microscope to see if the individual characteristics correspond.

Figure Bullet stria comparison



Figure . Cartridge case comparison (JFK assassination)



American courts have admitted firearms comparison testimony routinely for over 130 years, with reported cases beginning with Wynn v. State.359 Any early hesitancy about its admissibility had all but disappeared by the 1930s,360 when the pioneer firearms scientist Calvin Goddard, perfected the comparison microscope.361 Expert testimony that a found bullet or cartridge and a test bullet or cartridge originated from the same gun has now been admitted in every U. S. jurisdiction.362

Toolmark evidence may be susceptible to a viable Daubert challenge. The questions primarily arise in two areas, the claimed uniqueness of toolmarks and the standards by which experts may testify that toolmarks on two items agree or correspond sufficiently to claim a common origin.

On the uniqueness question, the National Academy of Sciences 2008 ballistics report concluded that "The validity of the fundamental assumptions of uniqueness and reproducibility of firearms related toolmarks has not yet been fully demonstrated."363 The report went on to state that "A significant amount of research would be needed to scientifically determine the degree to which firearms-related toolmarks are unique or even to quantitatively characterize the probability of uniqueness."364

The standards, or lack thereof, for determining whether the marks on two items agree is of greater concern. Experts agree that there is no perfect match.365 The Association of Firearms and Tool Mark Examiners (AFTE) states that the marks must be of "sufficient agreement" and only defines that phrase as "when it exceeds the best agreement demonstrated between tool marks known to have been produced by different tools and is consistent with the agreement demonstrated by tool marks known to have been produced by the same tool."366 The circularity of this "standard," and the lack of more definite criteria, has been the subject of criticism.367 And the expertise of firearms and toolmark examiners to make reliable comparisons has been steadfastly defended by its practitioners.368

Like fingerprint and other impression testimony, the testimony of toolmark experts is, in the final analysis, subjective. The 2009 NRC report is critical of the scientific basis for the type of toolmark and ballistics evidence that has been routinely accepted by the courts because “not enough is known about the variabilities among individual tools and guns” and because “[s]ufficient studies have not been done to understand the reliability and repeatability of the methods.”369 The Academy report found that a “A fundamental problem with toolmark and firearms analysis is the lack of a precisely defined scientific process" and noted the "heavy reliance on the subjective findings of examiners rather than on the rigorous quantification and analysis of sources of variability."370

Recent Daubert hearings have not resulted in a successful attack on classic firearms expert testimony. Of course, such testimony remains subject to attacks on the propriety and reliability of the laboratory procedures utilized or the qualifications of a proposed expert witness in a particular case and may require the trial judge to hold preliminary hearings into those matters to determine if they pose admissibility questions or only go to the weight of the government's evidence. In two recent Massachusetts cases, the courts conducted lengthy Daubert hearings to determine the admissibility of firearms expert testimony. 371 In United States v. Montiero, the court reviewed the Daubert requirements at length and found that firearms testimony was generally admissible but that the government's proffered witness was not qualified.372 Moreover, the judge held that even a qualified government expert "may testify that the cartridge cases were fired from a particular firearm to a reasonable degree of ballistic certainty. However, the expert may not testify that there is a match to an exact statistical certainty."373 Even with this limitation, there are no reported cases that reject the fundamental assumptions of firearm or other toolmark testimony based on a Daubert analysis.
2010-07-19 18:44 Читать похожую статью
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • Контрольная работа
  • © Помощь студентам
    Образовательные документы для студентов.