For four agonizing hours, Mark Zea stood outside the Borderline Bar and Grill near Los Angeles, waiting to learn if his youngest daughter, Camille, had survived an assault by a gunman that killed 12 people and left one wounded before the attacker took his own life.

It was after 3 a.m. on Nov. 8 when Camille, 18, used a friend's cellphone to call Zea to let him know she was alive and physically unharmed. Zea, a retired Los Angeles County Sheriff's Department deputy who now teaches medical terminology and police science at a Los Angeles area high school, was relieved, but also worried about Camille's psychological well-being. A couple of days after the mass shooting, Zea took Camille to Palm Springs, California, to unwind. When he suggested they see the movie "Bohemian Rhapsody," to his surprise she said no – she feared being in a crowd. That weekend, Camille was also uneasy at a Veterans Day parade. She told her father that she wasn't too fond of veterans at the moment; the Borderline killer was a Marine veteran.

Camille Zea, in the white skirt, and her friend Maria Davila in the Borderline club minutes before a gunman stormed in and fatally shot 12 people. Both girls escaped. Camille is struggling with the psychological effects of the attack. (Courtesy of Mark Zea)

Things didn't get better for Camille on her first day back at her high school, where she's a senior. She met with a school counselor, who invited Camille into her office to check on her well-being. Camille threw up. "Everything about a public space now gets me so scared. Going to school, I'm constantly watching my back," Camille says. "Going to Starbucks, I'm constantly watching my back. It really has, for now, destroyed my life. I don't feel safe going anywhere, nor do I want to go anywhere."

The consequences of the Borderline attack extend to Camille's father, who constantly worries about Camille's safety. Zea retired from the Sheriff's Department in 2002, after a standoff with a shotgun-wielding man who turned the weapon on himself. Zea was tired of the violence, of having to carry a gun. Now, "I almost feel compelled to carry a gun again," he says.

The Borderline shooting's effects on Camille and her father are a textbook example of how the consequences of gun violence often radiate beyond the immediate victims who are shot and killed or wounded, says Dr. Aaron Wilson, chief medical officer at Sierra Tucson, a residential treatment center in Tucson, Arizona, that treats, trauma, depression and other disorders. For many years, many medical professionals considered trauma to be something experienced by combat veterans, survivors of sexual assault and other individuals who had been directly affected by violence. "We're starting to realize the ripple effect is a lot bigger than we (previously) thought," Wilson says. The effects of such trauma can include anxiety, depression, feelings of sadness, fear of being in public spaces, hyper-vigilance, difficulty concentrating, being easily startled, flashbacks, nightmares and other sleep disturbances, Wilson says. Every person reacts differently to gun violence, he says. Some witnesses, bystanders and survivors of gun violence may experience brief periods of increased stress and anxiety while others go on to develop post-traumatic stress disorder.

It's impossible to quantify how many people who aren't direct victims are psychologically affected by gun violence. There's not much research on the topic, experts say. However, based on the high levels of violence in the U.S., the number may be in the tens of thousands, perhaps higher, Wilson says. "We are beginning to understand how big and far-reaching the ripple effect can be," Wilson says.

In the U.S., about nearly 110,000 people – enough to fill a large football stadium and two major sports or concert arenas – are killed and wounded annually in gun-related incidents, according statistics from the Centers for Disease Control and Prevention's National Center for Health Statistics. More than 38,000 people died of gunfire in 2016, according to the CDC. About two-thirds of those deaths were from suicide. Meanwhile, more than 67,000 people are injured by firearms annually, according to the National Electronic Injury Surveillance System.

Beyond these victims, the effects of gun violence can extend beyond people who are shot and wounded, witnesses, bystanders and family members of the injured and killed, says Hengameh Mahgerefteh, a psychologist based in Los Angeles who works with victims of gun violence. For example, in late October, a gunman killed 11 worshippers in a Pittsburgh synagogue; the attacker, who was arrested by police, allegedly told an officer he "wanted all Jews to die," according to a criminal complaint filed by law enforcement authorities. In the wake of the attack, an elderly patient, a Jewish woman, told Mahgerefteh she was fearful of going to her synagogue in Los Angeles. "She was afraid of going to a location that's supposed to be a safe place to pray and worship," Mahgerefteh says.

While some people who aren't in the proximity of gun violence can nonetheless be traumatized, typically the closer someone is to the gunfire or to a victim of gun violence, the greater the level of trauma, says L.A. Barlow, a certified psychologist with Detroit Medical Center. Shanda Smith, of the District of Columbia, is a case in point. In December 1993, Smith's son, Rodney, 19, and her daughter, Volante, 14, were shot to death as they sat in a car in Southeast Washington. A police investigation determined the killers, members of a D.C. drug gang, mistook Rodney, a college student who was visiting on Christmas break, for a rival. "I cried for like three whole years," Smith, 58, says. "I couldn't control my tears." Today, Smith says, she still thinks about her slain son and daughter, but she also has joy and laughter. Smith says that over the years she prayed vigorously but never sought mental health treatment because she was afraid city officials would take away her two younger boys if they learned she was seeing a psychologist or psychiatrist.

Getting prompt mental health treatment following exposure to gun violence can help head off or mitigate the effects of such trauma, says Mark D. Smaller, a clinical social worker and psychoanalyst based in Saugatuck, Michigan, and a recent past president of the American Psychoanalytic Association. In 2002, Smaller created a program at an alternative high school near Chicago that provided therapy in school to the students, many of whom had been in a gang and had been exposed to gun violence. Some had witnessed shootings, some had been shot at or shot and wounded, and some had been shooters. The program provided on-on-one and group therapy. "Most of the students would begin to heal from the impact of (their) trauma," Smaller says. It was important to begin therapy promptly. "The sooner you intervene with someone who's been traumatized by gun violence, the greater the odds you can reduce the probability of negative long-term impact of that trauma," Smaller says.