The Federal Witness Protection Program has been in existence since 1970. Its main purpose is to allow the government to have a better chance of getting witnesses to testify against people who might be inclined to harm those who testify against them. This is especially important in the prosecution of people who are allegedly involved in drug trafficking and/or organized crime.
In such cases, witnesses (especially those who once belonged to the organized crime families or drug cartels) are often afraid that they will be killed if they testify. This makes it hard to persuade them to testify as to what they know. The witness protection program was set up so as to protect these witnesses by giving them new identities that, it is hoped, will prevent them from being found and killed for their role in the trial.