Criminals use stolen guns (surprise!). So how can antigunners get political capital out of that? Push laws that will punish the theft victim if they fail to report the theft.
Why wouldn't someone report a theft? Well, they'd have a little incentive if anyone cared. Twenty or so years ago I had a pistol stolen from the glove compartment in my VW bug. I called in a report, and it was noted. I pointed out that the glove compartment door was glossy metal, would probably hold great fingerprints. Dust it, get my prints and deduct those, and you have those of the thief. The police said they didn't have enough time. I offered to drive to the central police station and park in their lot, so the fingerprint tech had only to come outside and dust. Naw, they said, the fingerprints will already have "evaporated." Yeah, sure, they evaporate. I gave up.
I'm told that shipments to dealers are often stolen in transit (which screws up recordkeeping and tracing, BTW). So why not crack down? Dealers and gunowners would love it. Shouldn't be too hard to compute out the distribution nodes where guns vanish. Or to park a few radio locators in, say, the buttstock of military-type rifles. Of course that doesn't lead to more legislation -- just to solving the problem.
[UPDATE, response to comment: it was a fingerprint tech with Tucson Police Department who told me the fingerprints would have evaporated (by the next morning, incidentally). It was a pretty clear brush-off. A year or so later I had an attempted breakin, where someone had tried to jimmy open a window. I figured they'd probably left some prints on the glass, but again couldn't convince anyone to dust for them -- they said they'd file the report and that was all they could do. To be fair, in that case I couldn't take the window down to the police station. But I'd have thought a stolen gun was cause enough to dust a car sitting in the police station parking lot!]
ANOTHER UPDATE: Naw, not much odds of civil liability here. Courts have gone against holding law enforcement liable for failure to prevent crime, on the basis that then law enforcement agencies would be liable to countless lawsuits. (I can see that, although in severe cases, such as Warren v. DC -- where a 911 dispatcher promised women that help was on the way, and then didn't even send out a radio report, with result they were subjected to 14 hours of rape and abuse -- you might think they'd recognize an exception).
I played a role in initiating the first successful suit against a parole board that let loose a dangerous guy -- gad, now I forget the case, but it concerned a murderous psychotic who had five psychiatrists opine that he was dangerous, and the parole board, composed of political hacks, let him out anyway, and he went on to commit a few murders in the Brown Fox Tavern. I think his name was Mitchell Blazak, something like that. I was a young pup law student clerking for a firm here, back in 1973 or 74, and got a memo on the case. The attorney wanted to sue the tavern owner for not giving in to the robber's demand, and I thought there was no case there -- no duty to yield to a criminal demand. But the robber's name stood out, and I realized I'd just seen an opinion from a State court upholding his conviction for attempted murder. Pulled out the opinion -- his conviction had been affirmed only a few months before the later robbery -- what gives here? Investigated, and argued to the attorney that there might be a case against the parole board for turning him loose. He went with it, it went to the Ariz. Supreme Court, and they held the parole board might be liable if gross negligence could be proven.