Connecting the Dots: The Science of CSI

Connecting the Dots

The Science of CSI


Calvin Goddard examines a revolver using a helixometer, an instrument he co-invented with colleague, John Fisher. The helixometer utilized a telescope that inserted into a gun barrel to determine whether the weapon had been fired recently, its rifling pattern, and the condition of the barrel. Image source: Goddard, Calvin H. “Who Did The Shooting?” Popular Science, vol. 111, no. 5, 1927, pp. 21-22, 171.

Calvin Goddard

Calvin Goddard began his career as a physician at Johns Hopkins University and then worked in army ordnance during WWI. In 1925, Goddard helped establish the Bureau of Forensic Ballistics, an independent crime lab in New York City. Dr. Goddard gained national prominence in the 1920s with his forensic studies in the Nicola Sacco and Bartolomeo Vanzetti murder case in Massachusetts (Goddard proved Sacco’s gun was used in the crime) and in the investigation of the 1929 St. Valentine’s Day Massacre in Chicago (Goddard showed that Chicago police officers were not involved in the murders). Later that year, Goddard established the Scientific Crime Detection Laboratory of Northwestern University in Chicago. It served as a model for the FBI crime lab established two years later.

Before and after photographs of bullets. The bullets on the right (B and D) have been fired. Note the striations along the fired bullets made when the projectiles passed through the barrel of the gun. Image source: Burrard, Gerald. The Identification of Firearms and Forensic Ballistics. Herbert Jenkins, 1951. View Source

Gun Barrels & Bulllets

The barrel of each gun has unique helical grooves that spin the bullet. These grooves also make impressions on the bullet as it passes through the barrel. Firearms experts will often test fire a crime weapon (usually in a water tank) to compare the projectile’s impressions with a bullet from the crime scene. Investigators also examine firing pin impressions (when a pin hits the primer and makes the cartridge explode), breech marks (when the cartridge is pressed against the end of the barrel), and ejector marks (when the cartridge is discharged from the barrel).

Though he did not invent the comparison microscope, Calvin Goddard was the first to popularize its use in forensic ballistics. A comparison microscope is made up of two compound microscopes bridged with a comparison eyepiece that places the fields of the microscopes side-by-side.

Photographs of two fired bullets, one from a crime scene, the other from a test firing. A comparison microscope enables an investigator to match striations in bullets. Image source: Burrard, Gerald. The Identification of Firearms and Forensic Ballistics. Herbert Jenkins, 1951. View Source