There are various federal statures. Consult with a lawyer.
I am a former federal and State prosecutor and now handle criminal defense and personal injury/civil rights cases. Feel free to check out my web site and contact me at (212) 577-9797 or via email at Eric@RothsteinLawNY.com. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. The above answer is for informational purposes only and not meant as legal advice.
A federal crime is a crime defined by federal law, that is to say, by act of Congress, ahd prosecuted by the federal government in the federal court. The same conduct might be proscribed by both federal and state law. When the federal government prosecutes the conduct in federal court it is for a federal crime. When the state government prosecutes the conduct in state court it is a state crime.
If you have information about a federal crime that you want to bring to the attention of the authorities for investigation and possible prosecution, you provide your information to the appropriate agency. The general federal law enforcement agency is the FBI. Other agencies have specialized areas of concentration. For example, you could report crimes involving postal matters to the FBI or to the postal inspector, and you could report drug crimes to the FBI or to the DEA. Ultimately it is the United States Attorney who decides whether to bring a federal prosecution.
I agree with Mr. Sachs. A federal law is an act or misdeed that is specified in the federal law which the US Attorney prosecutes. If you believe that someone has committed a federal crime, you should call the FBI or the US Attorneys office and make an appointment for an interview with either of them. They, in turn, will put all the paperwork together and you would then have to sign it under oath (thus making you responsible in case you're not telling the truth) and then they will issue an Arrest Warrant for that person's arrest if they believe your complaint and wish to go forward with a prosecution. You would be well advised to speak to an attorney who practices federal criminal defense law in advance to make sure you don't get in "over your head" and then regret it later.
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