School shootings have erupted in small rural communities and major urban centers across the U.S. over the past decade. According to an analysis of all mass shootings by a group called Everytown for Gun Safety, about 11 percent of cases involves possible mental illness and in 44 percent of the cases, the shooter committed suicide. Everytown is a coalition of government officials, victims and advocates against gun violence.
Here is a look at some of the worst school shootings in recent years:
Sept. 28, 2016 in Anderson County, South Carolina: A 14-year-old boy was charged with shooting a teacher and two students at Townville Elementary School after killing his father. One of the victims, 6-year-old Jacob Hall, eventually died from his injuries.
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Sept. 8, 2016 in Alpine, Texas: A freshman shot a fellow student at Alpine High School, then fatally shot herself. Police later said the girl wanted to kill her stepbrother but shot and wounded the junior, who found her with a 9-millimeter semi-automatic handgun in the girls' restroom.
May 5, 2016 in Prince George's County, Maryland: Eulalio Tordil is accused of fatally shooting his estranged wife, outside High Point High School to pick up their daughters, and a good Samaritan, then shooting four others a day later amid a massive manhunt. A former federal security officer, Tordil has been charged with three counts of murder and two counts of attempted murder.
October 9, 2015 in Flagstaff, Arizona: A confrontation between two groups of people at Northern Arizona University ended with one student was killed and three wounded after a freshman opened fire, police said.
Oct. 1, 2015 in Roseburg, Oregon: A gunman opened fire, killing nine people and dying in a shootout with police at Umpqua Community College. A government official says the man was 26-year-old Chris Harper Mercer. One witness said he demanded to know students' religion before shooting them.
May 14, 2015 in Jacksonville, Florida: Edgar Robles, 16, has been charged with second-degree attempted murder for shooting into a Jacksonville school bus and injuring two girls. Officials say Robles and some friends got into a fight with some teenagers on the bus about another person who had died. As the bus pulled away, at least three shots were fired.
Feb. 4, 2015 in Frederick, Maryland: Two men were arrested a month after a shooting outside a high school basketball game that injured two teenage boys. Brandon Tyler, 21, and Chandler Davenport, 19, each face assault and gun charges. Police say the shooting was gang related and that the men and their victims knew each other.
Dec. 12, 2014 in Portland, Oregon: A suspected gang member opened fire on a group outside an alternative high school, injuring four people. Three young people have been arrested in connection with the shooting. Two of them had a prior criminal history. The third pleaded guilty in May and has been sentenced to serve 10 years in a youth prison.
Oct. 24, 2014 in Marysville, Washington: Jaylen Fryberg, 15, killed three 14-year-old girls and a 15-year-old boy after inviting them to lunch in the Marysville-Pilchuck High School cafeteria. The depressed teen turned the gun on himself after killing his friends. Fryberg had sent a text message to a former girlfriend threatening to kill himself days before the shooting.
June 5, 2014 in Seattle: Aaron Rey Ybarra, 26, is charged with first-degree murder after a 19-year-old student is killed and two others wounded in a shooting at Seattle Pacific University. Ybarra's attorney has said mental illness was a factor.
May 23, 2014 in Santa Barbara, California: Elliott Rodger, 22, killed six people and injured 13 others in shooting and stabbing attacks near the University of California, Santa Barbara, campus. Authorities say he shot himself to death after a shootout with deputies. The shooter recorded a disturbing Internet video before the rampage, warning that he would slaughter those with a good life, especially women who had shunned him.
June 7, 2013 in Santa Monica, California: John Zawahri, 23, shot his father and brother and then shot at strangers in cars — killing three people — and then shot at people on the Santa Monica College campus. He was fatally shot by officers in the college library. Investigators say Zawahri was angered by his parents' divorce and they believe mental illness played a role in the killings.
Dec. 14, 2012 in Newtown, Connecticut: Adam Lanza, 20, killed his mother and then used three of her guns, including a semiautomatic rifle, to shoot 20 first graders and six educators at Sandy Hook Elementary School. Volumes have been written about his mental health problems since the Newtown shooting.
April 2, 2012 in Oakland, California: One Goh, 43, opened fire at a tiny Christian school, Oikos Univeristy. Goh was charged with seven counts of murder and three counts of attempted murder but is being held at a Northern California mental hospital after psychiatric evaluations concluded he suffers from long-term paranoid schizophrenia and is unfit to stand trial.
Feb. 14, 2008 in DeKalb, Illinois: Five students are killed and 18 were wounded when former student Steven Kazmierczak, 27, opened fire in a lecture hall at Northern Illinois University, before committing suicide. A year earlier, Kazmierczak had been a graduate sociology student at the school. Authorities say he started behaving erratically after he stopped taking his medication for an unnamed illness.
April 16, 2007 in Blacksburg, Virginia: Thirty-two people are fatally shot in a dorm and classroom at Virginia Tech, before the gunman, Seung-Hui Cho, 23, kills himself. He moved to the United States from South Korea with his family while a grade school student. Cho was in his senior year as an English major at Virginia Tech. It was the deadliest shooting rampage in American history and happened about eight years after 13 people died at Columbine High School in Colorado.