On Dec. 14, 2012, 20-year-old Adam Lanza fatally shot 20 children and six faculty members at Sandy Hook Elementary School in Newtown, Connecticut. Nearly four years after the tragedy, parents in the community have released a powerful gun violence prevention PSA, hoping to draw attention to the warning signs exhibited by troubled young adults.

The Sandy Hook shooting was the second deadliest school shooting in U.S. history, and the deadliest at a high school or grade school. Four years later, little has changed with regards to gun control legislation, and Republican members of Congress and the National Rifle Association continue to push the myth that civilians with guns can stop mass shooters.

In September, the FBI released a study of 160 active shooter incidents that occurred between 2000 and 2013 in the United States. Of those, "at least 107 (66.9%) ended before police arrived and could engage the shooter, either because a citizen intervened, the shooter fled, or the shooter committed suicide or was killed by someone at the scene," the Hartford Courant reported.

"[I]n only five of those incidents, however, did the shooting end 'after armed individuals who were not law enforcement personnel exchanged gunfire with the shooters.'" In 21 incidents, unarmed citizens "safely and successfully restrained the shooter," the FBI noted.

"I just want to make a point about guns fighting guns," Po Murray, a Sandy Hook mother of four said in a PBS News Hour special with the Newtown community.

"I don't think that worked out very well for Nancy Lanza," Murray said of the mass murderer's mother. "She owned six guns. And she's not with us, period."

Adam Lanza killed his mother before driving to the nearby Sandy Hook Elementary School where he killed 26 people and committed suicide once authorities arrived.

Murray is now the chairwoman of an all-volunteer grassroots organization called the Newtown Action Alliance and the Newtown Foundation. For the last four years, Newtown Action has sponsored a Sandy Hook Anniversary Trip to Washington D.C. every December 14. The event functions as a national vigil for victims of gun violence and is an opportunity for supporters of the families of victims and survivors of gun violence to meet with members of Congress.

"Adam Lanza and Nancy Lanza lived 100 yards from my home. And I was shocked and dismayed when I found out that they owned six guns, and many of them being assault weapons that, you know, created havoc in our community," Murray said.