It's always dangerous to challenge a wordsmith on a public forum, especially one who is in the process of canonization, going from Mr. Ed to Saint Edward, but here goes:
In my experience, state courts and state investigators, including municipal detectives, solve almost all fraud cases. The reasons are varied, and some background is necessary.
Almost all crime is a violation of a state law, be it code section, statute, regulation, etc. The federal justice system does have a place in investigating and prosecuting criminal and civil matters, but the numbers are tiny when compared to the state court venue, since most crimes are intrastate, not interstate, and not violations of federal law.
The founders set it up this way, partly as a compromise between the urban vs. rural factions. The 10th Amendment clearly states that all rights not specifically enumerated by the Constitution, or specifically forbidden to the states, remain the power of the states.
There is frequently a way to bootstrap a state violation into federal court, if the conduct crosses state boundaries, or has Uniform Commercial Code, i.e., federal law, implications. Imagine the difficulty for California, as an example, to prosecute illegal conduct that occurs not only in California, but several other states as well. Those fact patterns are where federal courts are the appropriate venue.
Many of us don't think about the cost of prosecution, whether state or federal. We just assume that our taxes pay for the justice system. That's partly true, since many states and the federal government fund their court systems from the general fund. However, there are other forces at work.
Prosecuting attorneys office all have a budget which controls operating costs. In many jurisdictions, the decision of whether to prosecute suspected fraud as a civil or criminal matter rests with the prosecutor. Unknown to many is that the prosecutor's office, whether District Attorney, state Attorney General, US Attorney's Office or other, usually shares in civil penalties awarded by the court. That means that when the District Attorney's Office of County of San Francisco is deliberating on whether to charge Corporation X criminally or civilly, they factor in the benefits of a potential fine to their office budget.
Of course, there are many factors considered when contemplating civil vs. criminal prosecution. Standard of proof is a major one: beyond a reasonable doubt for criminal vs. preponderance of evidence for civil. Unanimous jury agreement for criminal vs. a lesser ratio of agreement for civil, 9 jurors out of 12 for most civil trials.
Consider the numbers involved: there are about 1,200 postal inspectors that are charged with investigating violations of mail and wire fraud, USC Secs. 1341 & 1343. The Los Angeles County District Attorney's Office has almost 1,000 prosecuting attorneys, let alone investigators, paralegals, and other support people. There are approximately 2300 prosecuting attorney's offices throughout our 50 states and DC. That means there are probably 1,000 times the number of postal inspectors.
Not surprisingly, prosecutors operate by the 80/20 law: if you can get 80% of the benefit in sentencing a defendant using 20% of the time and energy, do it. That doesn't imply laziness. In fact, just the opposite. It shows an employee who wants efficiency, as there aren't enough hours in the day to investigate and prosecute every crime to its fullest.
Visit a state courthouse. Almost every major city and county has one. What do you see in the hallways? Raucous activity is what you see. Defendants and attorneys in serious conversation, with family members often nearby. Noisy, emotional, busy, and often tormented, that's the state court environment.
Now go visit a federal courthouse. Unless you live near one in a large city, you will likely have to research its location. What do you hear when you enter the halls of a federal courthouse? Silence. At first, you will think you entered before or after working hours, and that they are closed. Such is the rarified air of the federal judicial system.
All prosecutors look for low-hanging fruit, as I mentioned above. Wily defendants who are old hands at con games, and those defendants who hire expensive, competent counsel are treated differently than the typical small-time criminal, since matters of proof will be thoroughly checked by defense counsel, and the prosecutor will need to spend more time on the matter.
I have heard suggestions on this forum that the appropriate investigation of Specialty Auto-Sports should include RICO violations, wire and mail fraud, and involve various law enforcement agencies. I believe most of the suggestions are misplaced. Cons know the system. They spend their life perfecting their own brand of malfeasance and cheating others out of their money. They also know the judicial system. Why do you think Lawing is still in business? Because he takes precautions to appear as merely hapless or negligent, or the victim of circumstances, that's why. His goal is to minimize the appearance of the intent element in his crimes. What an accomplishment, and what a miserable way to go through life.
Apologies for the long digression, but I felt it was necessay.
So, Ed, if you have any proof or evidence of your postal inspector efficiency and contributions to fraud enforcement, please let me know your sources. I know you're a thorough researcher, and I'm always trying to learn more. However, absent source material, I'll stick to state prosecutions as a fraud deterrent.