Simple. John who has no record walks into a gun store and buys a gun legally. John then walks out of the gun store and goes to Bob's house, a prohibited person, with the legally acquired gun. John then sells Bob the gun that he ask John to buy (straw purchase). John then calls the sheriff and says the gun was stolen. Sheriff asks a few questions and lists the gun as stolen. Gun is found at a crime scene and John's name comes up on the OSP registry. Police question John again and he says it was stolen, he followed the law, reported it and has date, place, and officers name who took the report. They never catch Bob to question him so all they have is a stolen gun. Hard to prove it wasn't stolen and hard to prove John had anything to do with the crime because he was in Mexico on vacation when it happened and he can prove it.
See how easy that is? UBC solved absolutely nothing because Bob purchased the gun illegally.
How many times to you think John can get away with that?
FFl's have tried the "they were stolen" trick. Do it a couple of times and you get flagged and extra special scrutiny.
Have you been living under a rock somewhere? Why is it so hard to understand what a straw purchase is and why people do it?
I know exactly what a straw purchase is and why people do it. Today you don't even have to report the gun as stolen. You just say you sold it privately and you didn't get the guy's name. That is if you buy from a dealer. If you buy from a private individual there is no record at all.
If you are a gang in L.A. all you need is a clean cut looking guy in Vegas to buy guns face-to-face and drive them back to L.A.
When I was doing a few private sales a year I had people email me all the time trying to get me to sell them a gun without a CPL and DL. Guess who those folks were. Never mind, you probably don't know.
Those folks were prohibited people. You didn't sell them a gun but plenty of people will. They likely just moved on to the next ad until they found someone that didn't care or specifically wanted a completely anonymous sale.