School violence

Attendees hug before a program for the victims of the massacre at Columbine High School 20 years ago Saturday, April 20, 2019, in Littleton, Colo. (AP Photo/David Zalubowski)

A bouquet of flowers stands in front of one of the plaques in the memorial for the victims of the massacre at Columbine High School nearly 20 years ago before a vigil Friday, April 19, 2019, in Littleton, Colo. (AP Photo/David Zalubowski)

Protesters hold placards and gather to demand justice for an 18-year-old woman who was killed after she was set on fire for refusing to drop sexual harassment charges against her Islamic school's principal, in Dhaka, Bangladesh, Friday, April 19, 2019. Nusrat Jahan Rafi told her family she was lured to the roof of her rural school in the town of Feni on April 6 and asked to withdraw the charges by five people clad in burqas. When she refused, she said her hands were tied and she was doused in kerosene and set alight. Rafi told the story to her brother in an ambulance on the way to the hospital and he recorded her testimony on his mobile phone. She died four days later in a Dhaka hospital with burns covering 80% of her body. (AP Photo/Mahmud Hossain Opu)

Frank DeAngelis, center, who was principal at Columbine High School during the massacre almost 20 years earlier, fights back tears during a faith-based memorial service for the victims at a community church, Thursday, April 18, 2019, in Littleton, Colo. (Rick Wilking/Pool Photo via AP)

FILE - In this May 1, 1999, file photo, demonstrators gather on the Colorado State Capitol grounds in Denver, Colo., to protest against the National Rifle Association's annual meeting, which is being held in the city. Data shows that such shootings are less frequent and with fewer killed than in the years that preceded Columbine. Still, Americans worry about how safe schools are. (AP Photo/Eric Gay, File)

This combination of undated photos released by the Jefferson County, Colo., Sheriff's Office on Tuesday, April 16, 2019 shows Sol Pais. On Tuesday authorities said they are looking pais, suspected of making threats on Columbine High School, just days before the 20th anniversary of a mass shooting that killed 13 people. (Jefferson County Sheriff's Office via AP)

FILE - In this Dec. 14, 2012, aerial file photo, officials stand outside of Sandy Hook Elementary School in Newtown, Conn., where gunman Adam Lanza opened fire inside school killing 20 first-graders and six educators at the school. A Connecticut appeals court is scheduled to hear arguments on Wednesday, April 17, 2019, on whether parents of some of the shooting victims can sue the town for school officials' alleged failure to follow security protocols once the shooting began. (AP Photo/Julio Cortez, File)

This combination of undated photos released by the Jefferson County, Colo., Sheriff's Office on Tuesday, April 16, 2019 shows Sol Pais. On Tuesday authorities said they are looking pais, suspected of making threats on Columbine High School, just days before the 20th anniversary of a mass shooting that killed 13 people. (Jefferson County Sheriff's Office via AP)