One thing gun-rights and gun-control advocates agree on is that neither group wants guns in the hands of criminals. Stricter enforcement of existing laws, as well as stiffer penalties on buyers and sellers in so-called straw sales, would help.
Most gun-shop owners are law-abiding folks who try hard to follow the law. They conduct background checks, honor waiting periods, and refuse to sell weapons to people they suspect are going to resell or give the weapons to someone who is legally prohibited from purchasing a gun.
Most dealers at gun shows - the federally licensed ones as well as "occasional" sellers - also wouldn't knowingly sell a firearm to a criminal or someone they thought was going to give the weapon to a criminal.
But according to the Minneapolis Star Tribune, 90 percent of the guns used in crimes started out legally purchased but ended up in the illegal gun trade known as the "gray market."
Most of the guns on the gray market are obtained illegally on the street or from family members. A small but significant percentage - more than 8 percent - are bought by one person with the sole intent of giving it to someone who isn't legally allowed to have a firearm.
Sometimes, the path begins with a "straw" sale in which one person fills out the paperwork, undergoes the background check, and buys a gun from a licensed dealer, then hands the weapon over to a third party he or she knows couldn't pass a background check. That makes the sale illegal.
At other times, guns that end up on the gray market are bought at gun shows from occasional dealers who aren't required to do background checks. Federal law requires these dealers to refuse to sell to anyone about whom they have the merest suspicion that he or she might not be able to pass a background check. An investigation initiated by New York City Mayor Michael Bloomberg found that both licensed dealers and occasional sellers at seven gun shows - including four in Ohio - regularly ignored federal regulations.
Most straw buyers are women standing in for a spouse or boyfriend. The Minneapolis report said the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives is trying to trace all the illegal-sales history of every gun used in a shooting. But in a January report, the Milwaukee Journal Sentinel noted that the straw buyer usually gets no more than a slap on the wrist - probation or less than a year in prison.
Stronger penalties for straw buyers - more jail time, larger fines, or making them accessories to crimes committed with the guns they bought - might make them less inclined to purchase guns for other people.
It's often impossible to prove that a seller knows he's taking part in a straw sale. Even so, stiffer penalties likely would make even law-abiding dealers more alert and less likely to allow questionable sales.