When does the FBI decide to investigate a matter rather than the local or state police?
Many crimes are federal crimes as well as state crimes. The Feds tend to get involved in the more serious crimes. For example, if it’s a monetary crime, they get involved when there’s larger amounts of money involved. If there are federally insured banks involved, mortgage fraud, mail fraud, wire fraud, that sort of thing, healthcare fraud. Yes, the states usually don’t do that, but what you need to understand is that many crimes are both.
For example, a bank robbery is both a state crime of robbery or armed robbery as the case may be. It’s also a federal crime if the bank is federally insured. FBI gets involved in the more serious crimes or in certain political crimes where they are essentially instructed, “You take over and you investigate.”
For example, there are a lot of areas where local police are not trusted or are not competent to handle certain cases. Sometimes the FBI will get involved there. Not only the FBI, any of the federal agencies, all of which are law enforcement agencies and have full arrest and investigatory powers.