There are two well-known bodies in the United States that enforce the law on people. These are the CSI, which means Crime Scene Investigation, and the FBI, which stands for the Federal Bureau of Investigation. The CSI agency usually works with local law enforcement, while the FBI works mainly with the federal government. From this, you will notice that the FBI is involved in a broader aspect of the crime scene, and handles what might seem bigger than what the CSI agency can handle. The CSI, which are also referred to as the Forensic Science Service, can only be involved in and at the scene where a crime is committed, and nothing more.
The Crime Scene Investigation agency majorly carries out a deep scene investigation and also collects necessary information, after which they hand over the case to another agency to probe the case. Conversely, the FBI happened to be part of the Department of Justice and got its name changed to the Federal Bureau of Investigation from the Bureau of Investigation in the year 1935, though it has been in existence since 1908.