FBI Handbook of Crime Scene Forensics (5 page)

Comparative examinations can determine whether two metals or metallic objects came from the same source or from each other. Metal comparisons can identify various surface and microstructural characteristics—including fractured areas, accidental damage, and fabrication marks—to determine whether the objects share a common origin. Moreover, the manufacturing methods used to produce an object can be determined. These manufacturing techniques can include casting, forging, hot and cold rolling, extrusion, drawing, swaging, milling, grinding, spinning, blanking, ironing, deep drawing, and others. Examinations can determine mechanical properties, such as the response of a metal to an applied force or load. Examinations also can determine chemical composition, including alloying and trace elements.

The causes of failure or damage—such as the application of stress exceeding the tensile strength or yield limit of the metal; a material or manufacturing defect; or corrosion, cracking, or excessive service usage (fatigue)—can be determined. The magnitude of the force or load that caused the failure, how the force or load was transmitted to the metal, and the direction it was transmitted also can be determined.

Examinations can determine the approximate temperature to which a metal was exposed, the nature of the heat source, and whether a metal was in an electrical short-circuit situation.

Examinations can determine the method by which a metal was severed, such as sawing, shearing, milling, turning, or thermal cutting. The nature of the thermal source (e.g., burner bar, electric arc welder) used can sometimes be determined.

Examinations can determine how metal fragments were formed. If fragments were formed by impulsive (short-duration, high strain rate) loading, an examination can determine whether an explosive was detonated and the magnitude of the detonation velocity. The nature of the object that was the source of the fragments often can be determined as well.

Metallurgical testing of materials can determine whether inferior components were substituted in contracting frauds. The composition and mechanical properties of materials can be examined to determine if the components meet contractual obligations or appropriate regulatory codes. Precious-metal content also can be determined.

Examinations can determine whether a lamp bulb was incandescent when its glass envelope was broken. Determinations also can be made as to whether a lamp bulb was incandescent when it was subjected to an impact force such as a vehicular collision. Such determinations can be made even if the glass was broken by the impact.

The conditions causing a watch, clock, timer, or other mechanism to stop or malfunction and whether the time displayed represents a.m. or p.m. (calendar-type timing mechanisms only) can be determined. The on/off condition of appliance timers damaged by a fire or explosion often can be determined.

X-ray radiography can nondestructively reveal the interior construction and the presence or absence of defects, cavities, or foreign materials. The position of on/off switches and other mechanical components can be determined.

Questions concerning metallurgy evidence should be directed to 703-632-8441.
Follow the evidence submission directions, including
Requesting Evidence Examinations
and
Packaging and Shipping Evidence
.

• Samples must be sent with a Consent and Information Form for the National Missing Person DNA Database (FD-935 form). A copy of the law enforcement report should accompany the samples submitted.
  
• Collect samples in the following order of preference:
  
  1. Dried bloodstains.
     
  2. Buccal (oral) swabs.
     

Dried Bloodstains

Use the blood-cell collection kits that are available in FBI field offices or by contacting the NMPDD Program Managers at
703-632-7582
or
703-632-7586
.

Buccal (Oral) Swabs

• Use sterile, cotton-tipped applicator swabs to collect four buccal (oral) samples. Rub the inside surfaces of the cheeks thoroughly (use two swabs on each side).
  
• Air-dry the swabs and place them back into the original packaging or an envelope with sealed corners. Do not use plastic containers.
  
• Identify each sample with the date, time, subject’s name, location, collector’s name, and case number.
  
• Buccal samples do not need to be refrigerated.
  

Call the Laboratory prior to submitting bones, teeth, or tissue.
The communication accompanying the evidence must reference the telephone conversation accepting the evidence.

Skeletal Samples

Anthropological examinations can determine whether skeletal remains are human or animal. Race, sex, approximate height, and stature at death can be determined from human remains.

• Pick up samples with gloved hands or clean forceps.
  
• Air-dry samples and place in paper bags.
  
• Submit whole samples. Cutting skeletal samples increases the possibility of contamination.
  
• If possible, submit three samples.
  
• Submit skeletal samples with an anthropological report, preferably from an anthropologist certified by the American Board of Forensic Anthropology, or a medical examiner’s/ coroner’s report.
  
• Submit skeletal samples in the following order of preference:
  
  1. Femur.
     
  2. Tibia.
     
  3. Humerus.
     
  4. Teeth, skull, and/or mandible.
     
  5. Hand and foot bones.
     
  6. Lower arm bone.
     
  7. Vertebrae.
     
  8. Ribs.
     

Teeth

Personal identifications can be made by comparing teeth with dental records and X-rays.

• Pick up teeth with gloved hands or clean forceps.
  
• Air-dry teeth and place in paper bags.
  
• Submit teeth with an odontological report, preferably from an odontologist certified by the American Board of Forensic Odontology, or a medical examiner’s/coroner’s report.
  
• Submit teeth in the following order of preference:
  
  1. Nonrestored molar.
     
  2. Nonrestored premolar.
     
  3. Nonrestored canine.
     
  4. Nonrestored front tooth.
     
  5. Restored molar.
     
  6. Restored premolar.
     
  7. Restored canine.
     
  8. Restored front tooth.
     

Tissue

Tissue samples usually will provide sufficient quantities of DNA for testing.

• Pick up tissue with gloved hands or clean forceps.
  
• Collect 1-2 cubic inches of red skeletal muscle.
  
• Place tissue samples in a clean, airtight plastic container without formalin or formaldehyde and keep refrigerated or frozen.
  
• Label the outer container “KEEP IN A COOL, DRY PLACE,” “REFRIGERATE ON ARRIVAL,” and “BIOHAZARD.”
  
• Submit to the Laboratory as soon as possible.