Mieko Hattori continues to fight for her son, 20 years later.
In 1992 her teenage son Yoshihiro, an exchange student, was gunned down in Baton Rouge, La., after he accidentally approached the wrong house, dressed in costume, on his way to a Halloween party. Homeowner Rodney Peairs, who said he felt threatened, demanded the 16 year-old "freeze," but the warning was lost in translation.
When Yoshihiro failed to stop, Peairs shot him with a .44-caliber Magnum revolver.
"I'm embarrassed to say, I knew nothing about [the gun culture] in the US," Hattori said. "I thought, there's a lot of shootings in big cities - but my son wasn't going to a big city. I thought this wouldn't affect him."
Yoshihiro's case triggered outrage in Japan, where handguns are strictly banned. The case went to the Louisiana State court, where a 12-member jury acquitted Peairs of manslaughter, saying he acted in self-defense.
The heartbreak led Yoshihiro's parents to lobby for a change in US gun laws. They collected nearly 2 million Japanese signatures calling for tighter gun control, and personally handed them over to then President Bill Clinton. They donated compensation from their civil trial to anti-gun groups, and continue to support their efforts from afar.
Yet, on a recent trip back to Baton Rouge, Mieko Hattori said she was shocked to learn more than two dozen states had enacted "Stand your ground" laws that expand a person's right to self-defense.
The Connecticut shooting was a reminder of how little progress had been made.
"It was so heartbreaking to see so many young children killed, but I can't say I was shocked," she said.
"Guns only exist to kill people," said Masaichi Hattori, Yoshihiro's father.
The US and Japan sit on opposite ends of the spectrum on the gun debate.
While the second amendment guarantees the right to bear arms, Japanese law bans private ownership of handguns for ordinary citizens. People can legally carry a hunting rifle, but the process to get a permit requires rigorous checks: an application that lists a person's work and address history, family registry, a mental health checkup at a hospital, a background check on criminal history, a skills test every two years, and a training course for those using the rifle for sport. Some public safety commissions go as far as questioning an applicant's neighbors and co-workers, gun enthusiasts said.
Yoshiki Kobayashi, professor of policy management at Keio University, says Japan's resistance to guns stems from the 16 th century, when feudal lord Hideyoshi Toyotomi restricted the use of arms to the samurai class, though the current law was passed in 1958.
Japan remains home to one of the strictest gun laws and lowest gun-related crimes in the world. Eight people died from gun-related injuries last year, down from 11 the previous year, according to the National Police Agency. A quarter of the cases were tied to organized crime. (By comparison, from 2007 to 2009, the U.S. averaged 10,987 homicides per year by firearm, according to the United Nations' Office on Drugs and Crime.)
"The Japanese have a very different historical background. So, for most Japanese it's very difficult to understand the mentality in the US, and vice versa," said Kobayashi.
Kobayashi says comparing US and Japanese law is unfair, because the two sides operate on completely different premises.
That hasn't deterred the Hattoris from trying. In 1994, the two established a foundation in their son's name, to invite American high school students to study in Japan, and experience a virtually gun-free society. The students, 20 so far, have engaged in discussions with Japanese classmates, about the pros and cons of firearms.
"I know Japan can't be a model for the US right now," Mieko Hattori said. "But we can at least strive to eliminate guns."