I read in a paper that in Marylanmd they require that every handgun sold has a fired bullet casing deposited in some state record system. But not rifles, so it's no use in this case.

It seems a logical sort of idea, which could be applied right across the board, everywhere. And like Bobert I cannot begin to envisage how any responsible gun owner should have any objection at all. In fact I'd have imagined that they'd be the people promoting the idea in the first place. However the impression that comes across is that the gun lobby in the USA doesn't actually represent responsible gun owners. In the same way, you get motoring associations in England, such as the AA and the RAC, opposing measures that would save the lives of members.

Fingerprints aren't perfect either - you can wear gloves, and you even have people who've had their hands surgically altered. But it's caught a whole lot of people, because most crime isn't planned that well in advance, and that includes most shootings.