Fire investigation is one of the most difficult of the forensic sciences to practice. In most forensic disciplines, even the basic question of whether a crime has been committed is normally obvious. During a fire investigation, an entire process must be undertaken just to determine if the case involves arson or not. The difficulty of determining whether an arson fire has occurred or not arises because fires destroy evidence.

A fire investigator looks at what is left behind after a fire and obtains information to piece together the events that occurred in the moments leading up to the fire.

One of the challenging aspects of fire investigation is the multi-disciplinary base of the investigator’s job. Fires can be caused by or involve most things people see or use. For this reason, fire investigators need to know not only basic science of fire behavior, but knowledge of many different areas of study (including construction, electricity, human behavior, vehicles etc) is helpful. If the fire origin has, for example, a gas appliance, an investigator should know enough about appliances to either include or exclude it as a possible cause of the fire. Fire investigators must also know their own limitations and call upon experts to assist when needed. Accordingly, fire investigators sometimes work with forensic electrical engineers (when examining electrical appliances, household wiring, etc.) or others skilled in forensic engineering (gas-powered appliances, air handling equipment, gas delivery systems, etc.).

There are environmental influences that will affect decomposition. A body that is exposed to air will decompose more quickly and will have more insect activity. A buried body will decompose eight times slower than a body exposed to air. This is due in part to limited insect activity and possibly lower temperatures. Likewise a body submerged in water decomposes at half the rate of an exposed body. The rate of decomposition depends on the temperature of the water. Cold water will allow slow decomposition and warm water causes faster decomposition. The body is also shielded from insect activity as long as it is submerged.

A casting kit might include multiple casting compounds (dental gypsum, Silicone rubber), snow wax (for making a cast in snow), a bowl, a spatula and cardboard boxes to hold the casts.

If a Forensic Investigator finds a footwear impression in mud or dirt, she’ll photograph it and then make a cast. To prepare the casting material, she combines a casting material and water in a Ziploc-type bag and kneads it for about two minutes, until the consistency is like pancake batter. She then pours the mixture into the edge of the track so that it flows into the impression without causing air bubbles. Once the material overflows the impression, she lets it set for at least 30 minutes and then carefully lifts the cast out of the mud. Without cleaning the cast or brushing anything off it (this would destroy any trace evidence), she puts the cast into a cardboard box or paper bag for transport to the lab.

For toolmark impressions, a cast is much harder to use for comparison than it is with footwear. If it’s not feasible to transport the entire item containing the tool mark, a CSI can make a silicone-rubber cast and hope for the best. There are two types of tool marks a CSI might find at a crime scene:

* Impressed: A hard object contacts a softer object without moving back and forth (for example, a hammer mark on a door frame). The tool mark is an impression of the tool’s shape. It’s difficult to make a definite match with an impressed tool mark.

Striated: A hard object contacts a softer object and moves back and forth (for example, pry marks on a window frame). The tool mark is a series of parallel lines. It’s easier to make a definite match with a striated tool mark.

In toolmark analysis, the lab might determine what sort of tool made the mark and whether a tool in evidence is the tool that made it. It can also compare the tool mark in evidence to another toolmark to determine if the marks were made by the same tool.

Composite Art is an unusual marriage of two unlikely disciplines, police investigative work and art. The cop-artist, almost an oxymoron, possesses both skills. The artist can create a quality facial drawing with assured confidence. Though drawing skills are important parts of composite art, the real challenge is in the ability to interview and relate to a victim or witness. The purpose is to successfully gather, interpret and illustrate the information obtained from the victim’s memory.

In the past twenty years, the discipline of composite art has evolved into forensic art. The forensic artist possesses knowledge of victim psychology, post-mortem reconstruction and human aging. These artists currently use new computer technologies and digital imagery to create more successful investigative images.

Point of impact is the point of which some object strikes a bloody source. Point of origin is the three diamentional area where a bloody object is struck.

Shadowing and Ghosting

Shadowing and Ghosting occur when blood is sprayed around a room and there is an intervening target.

Swipe and Wipe are terms used when blood is put onto a surface, wipe’s occur when something that is not blood stained move through a bloody surface. Swipe’s occur when a bloody object moves across a non-bloody object.

Transfer Patterns

Transfer patterns occur when something bloody is placed on a surface and some form or recognizable shape is produced.

When blood drops fall into a blood drop that already hit a surface, the blood makes a satellite kind of shape. Other drops are usually made from that drop as well.

Expiratory blood,

Expiratory blood is blood is blood that come out of an air way or passage way as result of a cough or sneeze.

Cast off stains happen when an object with blood on it, is moving at a significant amount of speed and that blood hits a surface. Usually the blood is in a vertical line.

For the next three days I’ll be discussing 6 different Blood Spatter topics including,

Blood into blood

Expiratory blood

Point of origin

Shadowing/Ghosting

Swipe/Wipe

Transfer Pattern

The parallel search: All of the members of the CSI team form a line. They walk in a straight line, at the same speed, from one end of crime scene to the other.

The grid search: A grid search is simply two parallel searches, offset by 90 degrees, performed one after the other.

The zone search: In a zone search, the CSI in charge divides the crime scene into sectors, and each team member takes one sector. Team members may then switch sectors and search again to ensure complete coverage.

Silver nitrate is a component of black and white photographic film. When investigators expose a latent print to silver nitrate, the chloride in salt (sodium chloride) molecules present in the print residue reacts with the silver nitrate and forms silver chloride. This colorless compound develops, or becomes visible, when it’s exposed to ultraviolet light, revealing a black or reddish-brown print.

- Brandon Anderson

Tags: forensics, chemistry, ninhydrin, silver, nitrate