Serial killers have had a profound impact on the United States' most powerful law enforcement agency, the Federal Bureau of Investigation. Through a brief history of the FBI, the birth of the Behavioral Analysis Unit is highlighted and criminal profiling is realized as a tool to apprehend these serial killers. Four serial killer cases are presented as important representations to illustrate the contributions that were made to the FBI's investigatory procedure. As serial killings make up only one percent of the murders in the U.S. each year, it is still evident that these cases have had a profound impact on the U.S.'s top law enforcement agency. The FBI has been able to react to each case more effectively than the last. Constant learning on the job, as each impactful case happens within a short time span from the last, has been a necessity for investigators and has been a prime strength of the FBI. There is no way to tell when an individual will begin to commit serial murder, so while the FBI's methods are not perfect, the Bureau has been able to respond in full to each challenge a new serial killer case has presented and arrest the guilty party. Through an analysis of the criminal profile, stereotypes attributed to serial killers, and the application of forensic evidence to serial killer investigations, the impact of the investigations of these cases by the FBI is examined. A real world application of the FBI's recommended procedure for a serial killer investigation is spotlighted and analyzed to determine its practicality in modern-day investigations.