John, I'm guessing the case you're referring is the from which stems the Searcy v Dayton court case which cleared the Chief of Police of any liability due to his sign-off on an NFA transfer.
The original case which spawned the Searcy v Dayont lawsuit stems back to Roger Waller, a Dayton, Ohio cop. In 1988, he was approached by a neighbor about a drug house in a nearby neighborhood. Waller (off duty at the time of the incident) and the neighbor went to the house, entered it, and confronted the drug dealer in kind of a "Dallas SWAT" mode: guns drawn, shouting, hollering, etc... Waller was carrying, according to the court papers, "a MAC 11" submachinegun (most likely an M11/Nine, as if it even matters, and one that he'd had for several years prior to the shooting.) The gun dischared, killed the alleged drug dealer (who, by all accounts was a real jewel of humanity to begin with.) For the record, Waller pled guilty to murder and felony assault.
For the record though, even though the Waller case is often cited as being the only instance in which a legally possessed machinegun was used in a crime of violence by its legal possessor, it's is not the only instance.
I know for a fact of another case in Ohio, this time in 1996, wherein a Dr. Shou Chao Ho used a suppressed .380 M11 to kill a Dr. Carmelito Olaes. This murder happened in September, 1992 in Brunswick Hills township. I don't have a case number for you, but if you want it, I have a pdf scan of the newspaper article covering Dr. Ho's arrest. I'm also told of a case in Las Vegas (by a long-time Las Vegas FFL/SOT) of a case wherein a local attorney went into to a casino and tried to rob it with his registered MP40. Apparently, his defense was that he only to do a suicide-by-cop, not rob or hurt anyone. (I'm told his defense flew out the window when it was revealed he wore body armor during the attempted hold-up.) I also recall a case from within the last four to seven years ago (based on how long I've known my wife and we've been married), reported in the Naples, Florida newspaper. I remember reading it, and even saving the article, but since the sale of house in Naples and my wife's subsequent move to VA, I haven't seen it. BUt I digress... In this case, I recall reading about how some knucklehead and his redneck buddy used a MAC 10 to shoot roadsigns while cruising down Alligator Alley one night.
There may be a few more of these types of crimes committed with legally-possessed MGs, by their registered owners, but I'm unaware of them. Of course, when held to the strict letter of the law, there are hundreds (perhaps even thousands?) of crimes committed with legally-possessed MGS, but they're generally of a procedural nature instead (ex., failing to file a 5320.20 to go out of state for a weekend, lending an MG to a buddy to go shooting in the afternoon, bound book mistakes, etc...) Regardless, your point that such instances are few and far between is entirely accurate.
