Final answer:
The estimation of the number of serial killers in the last century is around 200-500 based on studies and research conducted by criminologists. The actual number may vary due to various factors such as the secretive nature of their crimes and the difficulty in linking cases.
Step-by-step explanation:
The FBI does not provide an exact number of serial killers in the last century. It's important to note that the estimation of the number of serial killers can be challenging due to various factors such as the definition of serial killer and the detection and reporting of their crimes. However, based on research and studies, criminologists estimate that there have been around 200-500 serial killers in the last century.
This estimation takes into account documented cases of serial killers and those who have remained unidentified. It's worth mentioning that the actual number may vary due to the secretive nature of their crimes and the difficulty in linking cases that may not have been detected or connected.
Serial killers are a complex subject and studying their behavior and motives helps in understanding criminal psychology and enhancing criminal investigations.