Do local police initiate any federal crime investigations or do they always refer them to the feds?

How about vice versa? Does the FBI ever get involved with state crimes?
Answers:
I represent a sheriff's department. We often initiate federal crime investigations and often do the entire investigation. The results of our investation are submitted to the District Attorney. The District Attorney consults with the U.S. attorney's office and the 2 attorneys' offices determine whether the crime will be prosecuted in state or federal court. State courts do have jurisdiction over federal crimes. State courts are the only courts of general jurisdiction and a federal crime is usually a state crime also. My county has 10 Indian tribes and those cases can only to tried in federal court, or in less serious cases, tribal court. We have entered into Mutual Aid Agreements with most of our tribes, so we have law enforcement power over lots of the Indian nations. The Indians never agree to state court jurisdiction. Unfortunately, our U.S. attorney was one of the attorneys fired by the administration so that office is in an uproar. I also noticed a case I thought was settled was set for hearing in federal court, so the federal judges in my jurisdiction are not feeling very friendly with the Department of Jusitice, but that's another issue. I believe most of the federal prosecutions in my county are initiated by the local sheriff. How long he stays in the investigatory position is determined by consultations with the local District Attorney, the U.S. attorney and the FBI.

---

Law enforcement agencies can motu proprio investigate cases when their personnel has personal knowledge that person/s committed crimes even without a complainant.

---

The local police just respond to what they're told to. They're the first call.

---

Local police investigate crimes based on either complaints from citizens or their own observations. Prosecutors decide whether the evidence presented by the police is best handled under state or federal law. If a local prosecutor or police department finds evidence that suggests a federal violation, they ordinarily will contact the office of the U.S. Attorney in their district, and the U.S. Attorney will coordinate the response, and ultimately decide whether the prosecution should be state or federal, or whether additional investigation is required.

If there is additional investigation required and the crime is apparently federal, most often the U.S. Attorney will request that the local FBI office get involved.