(CBS News) WILMINGTON, Del. -- To understand how guns get into the hands of the mentally ill, look no further than the case of 68-year-old truck driver Ronald Williamson. He's charged in the murder of his 55-year-old acquaintance during a hostage stand-off in Greenwood, Del., in 2011.
Williamson had been committed to a mental institution two years before, and under Delaware law, he was barred from purchasing a gun. But he had no trouble buying a gun during a trip out of state, where there was no record of his mental illness.
"Why is it that somebody in one state can't buy a weapon because of a mental illness -- why should they be able to go across a border, a five-minute drive, to buy a weapon elsewhere?" asks Delaware Gov. Jack Markell. "It doesn't make any sense."
So Markell teamed up with Captain Jason Sapp of the state police to convince the Delaware legislature to change the law.
"It's going to minimize the number of firearms that fall into the wrong hands," Sapp says. "Simple as that. I could only wish that every state in the country would move towards that type of information sharing for everyone's benefit."
Delaware has now reported to the FBI database over 19,000 names of people who've been declared mentally ill by a court or involuntarily committed to a mental institution. That's the second-highest reporting rate in the nation, right behind Virginia. Those names are now accessible in background checks at gun stores across the nation.
"The point is, one name that's reported could literally save lives, which is why we've taken this on so seriously," Markell says. "It's why we worked hard against significant opposition."
Watch: How did Minn. murderer get permit to buy 15 guns?
Reporting to the database is voluntary for states and often incomplete. Thirteen states -- Alaska, Massachusetts, Wyoming, Hawaii, Louisiana, South Carolina, Mississippi, Rhode Island, South Dakota, Vermont, Oklahoma, New Hampshire and Montana -- told us they are not reporting any mental health records to the FBI.
"The quality of the national database is only as good as the names that are submitted to it," Markell says. Asked what other states can learn from Delaware's experience, he says, "There are two things that they can learn: first of all, it's effective, and second of all, it's easy to do. It only took us 90 days to get this done."
The mental health database is growing. In 2004, gun stores had access to 200,000 names. Today, there are 2.5 million names. But a recent study funded by the Justice Department estimates the database does not contain the names of two million others who've been declared mentally ill.