ATF Certified Fire Investigators (CFIs) are the only investigators trained by a federal law enforcement agency to qualify as expert witnesses in fire origin and cause determinations.

Historically, fire investigators relied on a variety of indicators to determine how and where a fire started. The physical evidence that "defined" an arson was accepted as "fact" and used in court to support an incendiary cause for a fire. However, successful defense challenges to many of these indicators has required further scientific validation. ATF's CFI Program has taken fire investigation and analysis beyond a discipline based on experience and has applied scientific and engineering technology.

Through computer software programs, these agents can use mathematical equations to describe the chemical and physical behavior of fire. Computer modeling has proven successful in the courtroom. It has been used as an interrogation tool to verify what a witness or suspect has said and as a means to refute the testimony of a defense witness.

To become a CFI, an ATF special agent must undergo a 2-year training program that includes 6 weeks of class work, and examining 100 fire scenes under the mentorship of an experienced CFI.