Trigger warning: violent images

Sandy Hook Promise, a nonprofit started after the 2012 shooting at Sandy Hook Elementary School in Newtown, Connecticut, that killed 20 students and six adults, has released a chilling PSA today that hopes to prevent mass violence in schools.

The short film begins with a smiling teen boy, who opens his locker to get the perfect backpack that his mother bought him. The images then turn dark and the film ends with a young girl, crying as she texts her mother goodbye while a door opens and footsteps approach.

The "Back to School Essentials" public service announcement lists the things kids generally need to start the new school year. The items, however, serve a much more distressing purpose — to try to survive in the event of a mass shooting. Although the film warns that acts of violence can be prevented, it also illustrates the unnecessary fear that children face in a school setting.

As a student runs down a hallway, his face turns dark as he hears the screams of his classmates. "These new sneakers are just what I needed for the new year," he says as gunshots are heard in the background. Other students praise the usefulness of jackets in securing doors, skateboards in breaking windows, socks in applying a tourniquet and scissors in fighting off attackers.

In the final scene, a girl hides in a dark bathroom, texting anxiously on her glittering pink phone. "I finally got my own phone to stay in touch with my mom," she says with tears in her eyes as she texts "I love you" to her mother. Then, the door is heard opening and footsteps approach. The PSA ends with the tag line: "It's back to school time. You know what that means."

According to Nicole Hockley, managing director of Sandy Hook Promise, "It's meant to be an intense video." Her son, six-year-old Dylan Hockley, was killed in the Sandy Hook shooting. "This is what our kids are experiencing now in school," she says. "We wanted to focus on this back-to-school time because parents still think of it as this rosy time where you're getting your staplers, shoes, folders and binders. Whereas, it's back to a time of violence for a lot of kids."

Sandy Hook Promise hopes to empower schoolchildren so they can respond effectively in the event of a school shooting. When asked about the latest mass shootings in California, Ohio and Texas, and the fact that Congress has yet to act on gun violence, Hockley said the conversation around guns is slowly evolving.

"I think each time, sadly, we are moving closer to the time that it's going to be different (after a shooting). A lot has changed since Sandy Hook," she said. "The recent back-to-back shootings are so heartbreaking. The conversation continues to happen. More people are getting involved. Legislation is available in Congress right now that can start to chip away at these acts of violence. Prevention, plus legislation, that's the cure to this."

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Hockley believes that a universal background check bill that passed the House but is stuck in the Senate shouldn’t be cause for controversy. "I always have hope. I absolutely know that we can prevent this," she said. "I know we can stem this tide. We just need to keep chipping away."