It sounded like a large book falling, neighbors said. But it wasn't. It was the sound of a single gunshot that struck college student Megan Bookstaver in the head, Tarrytown police said. She and two others were "examining firearms" in an exclusive riverfront townhouse Monday afternoon when the gun went off, according to police. She was pronounced dead at the scene. One law enforcement source termed the shooting a "tragic mistake."

Many focus on the rights of gun ownership; we must continue to address the responsibilities. The death of Bookstaver, 23, adds to sad statistics that demonstrate the danger of keeping guns in the home.

The mere act of keeping a gun in the home exponentially increases risk for those who live -- or visit -- there. Various data demonstrate the added risk for suicide, domestic-violence homicide and accidental death in a home where guns are housed; such often-spontaneous acts are made more deadly by guns' efficiency.

In Monday's tragedy, the shooting victim was in a fourth-floor room along with her boyfriend Eric Gaulin, 25, who lived in the townhouse with his parents, and a third, unidentified person. Law enforcement sources told The Journal News that Gaulin and Bookstaver were gun enthusiasts and often went target shooting.

Bookstaver, a student at Mercy College and a Long Island resident, was shot by a "long gun," which does not require a permit in New York. Police say other long guns were found in the home.

What works

After the Sandy Hook Elementary School slaughter, many states, including New York, instituted tougher gun-safety regulations. But what legislative measures work best to stem gun deaths? Research into effective measures remains scant.

The federal Centers for Disease Control and Prevention halted medical research on gun violence in 1996, when Congress yanked funding for such research by the CDC's injury prevention center. President Barack Obama has revived some of that research -- part of the 23 executive orders in the wake of the Newtown, Conn., school massacre -- but we pay a price for the lull.

The nonprofit ProPublica public-interest journalism website explored what the earlier CDC research documented, and what work remained.

"What the research showed was not only did having a firearm in your home not protect you, but it hugely increased the risk that someone in your family would die from a firearm homicide. It increased the risk almost 300 percent, almost three times as high," Dr. Mark Rosenberg, former director of the CDC's National Center for Injury Prevention and Control, said in a February interview with ProPublica.

The next step: figuring out what safety measures would save the most lives. "It's not one, two or even three things that are really going to solve the problem. They may salve our conscience, but they wont solve the problem," Rosenberg told ProPublica. "The research is really, really important. We really need to find out what works, so that we can save more lives."

According to the Small Arms Survey by the Geneva-based Graduate Institute of International and Development Studies, Americans own 270 million guns.

Many gun owners understand the risks, and follow all safety rules. There is no room for exceptions. All gun owners must make better choices, to protect us all.