FOR Exam III - Firearms and Digital Forensics

What are the two categories of firearms?

Long guns and handguns

What are the types of handguns?

Single-shot pistol (one round at a time), revolvers (several firing chambers in a revolving cylinder), and semi-automatic pistols (removable mag and one shot per trigger pull).

What are the types of revolvers?

Swing-out revolvers (cylinder swings out exposing chambers), Break-top revolvers (barrel and cylinder swing down to expose loading cylinder), and Solid-frame revolvers (chambers loaded individually through a gate on the right side of the frame)

What are the types of long guns?

Shotguns (ball-shaped projectiles called “shot”, smooth barrel, narrowing of barrel (called choke) can concentrate shot when fired), and rifles (barrel with grooves and lands, ammo is impressed with grooves and lands when fired)

What is a gun barrel and what are gun barrel markings?

Barrel is produced by a solid bar of steel hollowed out by drilling. Rifling is the act of impressing the inner surface of the barrel with grooves.

What are striations?

Lines found in the interior of the barrel. They form the barrel’s individual characteristics. No rifled barrels will have the identical striation markings.

How does firing a gun actually work?

The trigger being pulled hits a hammer which releases the firing pin, causing it to strike the primer, which ignites the powder.

How does computer imaging play into firearms?

The National Integrated Ballistics Information Network (NIBIN) has files from bullets and casings recovered from scenes and test fires from retrieved firearms. Ultimate decision falls on examiner via microscopic methods.

How can you determine distance with a suspect weapon?

The distribution of gunpowder particles and other discharge around a bullet hole allows analysis of the distance from where it was fired. To test it, the suspect weapon is fired from various distances at a target.

What shape will a contact or less than 1 inch from the target shot be?

Star-shaped (stellate) tear pattern around the bullet entrance. Powder gets less concentrated the further away from the target.

How do you determine distance when a shotgun is involved?

Pay attention to the type of suspect weapon and ammo. If you have no weapon, muzzle-to-target distance can be estimated via using the spread of the discharged shot. (as shot distance increases, pellets separate and spread out)

How do you test for gunshot residue?

To test garments, surfaces of items are examined microscopically for the presence of gunpowder residue. To chemically test, the Griess test involves heat releasing the nitrite and turning orange.

How to test the suspect’s hands for gunpowder residue?

Check for barium and antimony using an adhesive stub. (check palms and backs of hands near thumbs)

What test helps you see the morphology and elemental analysis of gunpowder residue?

A Scanning Electron Microscope (SEM) with and X-ray analyzer.

What are some tips for firearm evidence collection?

Firearms can be handled where fingerprints cannot be taken (serrations on slide and checkered stocks), NEVER package a loaded weapon, remove mag and make sure chamber is empty, use pure chain of custody.

What are serial numbers?

Unique numbers applied to each gun by the manufacturer. Serial Number Restoration is the restoration of an obliterated serial number by scientific methods.

What are the serial number application methods?

Dot matrix (engraved dots to make numbers), laser engraving (shallow and “burned” appearance), and stamped serial numbers (stamp hammered into object leaving a negative impression)

What is the theory of stamped serial numbers.

When the stamp is hit, plastic deformation of the metal occurs, leaving an impression. The compressed area of the at the base of the stamp is strained below the surface of the stamp. The depth of the strained area is dependent on the type of metal, but the purpose is to impart a PERMANENT number for identification.

How do criminals attempt stamped serial number obliteration?

They grind the metal to the lowest point of removing the number, which makes the visible part of the number be obliterated. They think that because that visible part is destroyed that the gun can’t be traced.

Why doesn’t stamped serial number obliteration work?

The number is no longer visible, but the stressed area underneath from the stamp is the reason serial number restoration is possible.

How can you restore a serial number?

Chemical etching. Steel is made mostly of iron and carbon. Copper salts are common to aid in the oxidation of iron process in acid etching. Hydrogen gas bubbles are produced, and the number can be seen.

What are the tips for serial number documentation?

Write it down and photograph in correct lighting. Chemicals used for etching should be specified in notes.

What are tool marks, and what are their characteristics?

Impressions, cuts, gauges, or abrasions caused by a tool coming in contact with another object. There are class characteristics (size and shape of tool), and individual characteristics (shape and pattern of imperfections being modified by damage)

Should the investigator try to match up the tool with the object with the tool mark?

No. Any contact can alter the mark and make evidence invalid. Comparison microscope is used instead.

What are examples of other impressions?

Shoe, tire, or fabric impressions. Should be photographed with and without scale before any interference.

What do you need to compare two findings?

A sufficient number of points of comparison. New computer software is helpful with matching up shoe and tire impressions.

What is digital forensics?

The application of computer science and investigative procedures for a legal purpose involving the analysis of digital evidence after proper search authority, clear chain of custody, and proper use of validated tools, reporting, and expert presentation.

What is the history of digital forensics?

The FBI’s Computer Analysis and Response Team (CART) was formed in 1984 to handle digital evidence. CART teamed up with the Department of Defense Computer Forensics Laboratory (DCFL) in the late 90s.

What does investigating digital evidence include?

Securely collecting data, examining data to determine origin and content, presenting digital info to courts, and applying laws to digital services.

What are the values of digital forensics?

Organized and detailed evidence, supports timelines and intent, more reliable than witness memory, factual and timestamped info, text/call logs.

What are the two categories of digital investigation?

Public-sector investigations which serve the government (cops, criminal activity, public safety) and private-sector investigations which serve individuals/businesses (infidelity, fraud, bg checks).

What’s the difference between a Digital Evidence First Responder (DEFR) and a Digital Evidence Specialist (DES)?

The DEFR responds to the scene, assesses situation, and takes precautions to preserve evidence. The DES analyzes the data and can call upon another DES.

What is the role of a digital forensics professional?

Gather evidence to prove a suspect committed a crime or violated a company policy. They can investigate the suspect’s computer and preserve evidence on a different computer. CHAIN OF CUSTODY

How does law enforcement help with digital forensics?

Computers can store information they need to determine the chain of events leading to a crime and the evidence itself. They need to follow proper procedure and know that digital evidence can be destroyed by an overeager investigator.

What is a basic digital forensics investigation plan?

-Collect evidence

-Complete evidence form and chain of custody

-Transport evidence to comp forensics lab

-Secure evidence in approved container

What are the challenges to digital forensics?

Massive data volume, lack of trained professionals, months long lab delays, and budget limits.