Lt. Ira Parnell demonstrates the use of the water recovery tank. The gun is fired through the hole into a funnel tank that extends down to the story below. The bullet is captured in a cup and sent for analysis. Photo by Natasha Whitling

Due to great interest in crime show dramas like CSI: Crime Scene Investigation , the Shepherd's Center of Columbia is holding a nine-week class called CSI: Columbia. The class features a different speaker each week who specializes in a particular field of criminal investigation.

Lt. Ira Parnell was born with the law enforcement gene. His father was Sheriff of Sumter County from 1952--1980, and his grandfather was a police officer. So it was probably no surprise to anyone when he decided to major in criminal justice at USC and later work at SLED.

Parnell, who has been working with SLED for 34 years, is a forensic expert in firearms. His department processes firearm and tool mark evidence from crimes of which SLED has been asked to consult.

Firearms leave distinct markings on bullets and shell casings, Parnell said, which can positively match fired bullets and material to the gun from which they were fired.

Tools also leave distinct marks on the hard surfaces on which they are used. Parnell explained that manufacturing and personal use and abuse of tools create marks on tools that make the tools totally unique and identifiable.

One of the tools SLED uses to process firearm evidence is their 4,000 gun reference library. The guns, some of which are on display at SLED, allow investigators to identify guns used in crimes.

Another tool SLED uses is a water recovery tank, which is used to test fire guns. Made of stainless steel and extending to the story below, the tank is filled with water to slow bullets down. After the gun is fired, the bullet falls to the bottom of the tank, where it is collected for analysis.

Typically, when test firing a gun used in a crime, SLED will test four different kinds of cartridges that could have been used with that particular gun. The fired bullets are then painstakingly observed under a microscope to determine if they match bullets and fired materials found at the crime scene.

SLED also tests shotguns for pellet spread. At close range, the pellets from a fired shotgun shell will be close together. At farther range, the pellets will be farther apart.

Knowing the distance from which a gun was fired can be important in cases of self-defense, Parnell said. Pointing to the door several yards away, he said, "From here to the door, you might not be in fear of your life, but from here to this chair, you might really be scared."

Next week in The Columbia Star : Alex Layton, SLED, trace evidence.