Serbian police officers of the Special Anti-Terrorist Unit pose for a picture in their base outside Belgrade October 8, 2014. When the killing of an unarmed black teenager by a white policeman in Ferguson, Missouri, in August sparked sometimes violent protests, the response of police in camouflage gear and armoured vehicles wielding stun grenades and assault rifles seemed more like a combat operation than a public order measure. Some U.S. police departments have recently acquired U.S. military-surplus hardware from wars abroad, but there are many law enforcers around the world whose rules of engagement also allow the use of lethal force with relatively few restrictions. But for every regulation that gives police wide scope to use firearms, there is another code that sharply limits their use. In Serbia, police may use measures ranging from batons to special vehicles, water cannon and tear gas on groups of people who have gathered illegally and are behaving in a way that is violent or could cause violence, but they may use firearms only when life is endangered. (Photo by Marko Djurica/Reuters)

A student of the Krasnoyarsk choreographic college prepares backstage before a dress rehearsal of a performance by graduates of the college at the State Theatre of Opera and Ballet in Russia's Siberian city of Krasnoyarsk, Russia, May 12, 2015. The annual performance showcases the work of students from across Russia who study or have studied at the well-known school. (Photo by Ilya Naymushin/Reuters)

An air raid drill at Seattle College caught students William Bates, left, and Edna Mae Farrell, right, while they were eating their lunch in the school café, but they simply took shelter under the table and continued eating in Seattle, Washington, March 17, 1942. Air raid wardens said 350 students left their classrooms and assembled in shelters within one minute in first at the college. (Photo by AP Photo)

A student wearing a face mask prays before the start of the annual college entrance examination amid the coronavirus pandemic at an exam hall in Seoul, South Korea, Thursday, December 3, 2020. South Korean officials are urging people to remain at home if possible and cancel gatherings as about half a million students prepare for a crucial national college exam. (Photo by Kim Hong-Ji/Pool Photo via AP Photo)

Jockey student Mariangelys Almedina (Front) balances on a steel drum suspended in the air by a series of springs to simulate riding a horse as Instructor Willie Lozano looks on at the Vocational Equestrian Agustín Mercado Reverón School located in the Hipódromo Camarero on November 17, 2022 in Canovanas, Puerto Rico. The Vocational Equestrian Agustín Mercado Reverón School has produced some of the best jockeys in the world but also prepares students for a wide range of equestrian jobs on a tuition-free basis. (Photo by Al Bello/Getty Images)

Students of JSS Dutse Alhaji participate in a cultural dance performance during celebrations to commemorate Nigeria's 55th Independence Day in Abuja, Nigeria, October 1, 2015. (Photo by Afolabi Sotunde/Reuters)

Tibetan students play at a class break at the Xiangnong primary school on April 15, 2005 in Kangding County of Ganzi Tibetan Autonomous Prefecture, Sichuan Province, southwest China. There is only one teahcer in the Tagong Village, 12 Tibetan students get free education from him in Xiangnong primary school. (Photo by China Photos/Getty Images)

Students are seen on a pickup truck at the agricultural road which leads to the capital city of Cairo, Egypt, October 13, 2016. (Photo by Amr Abdallah Dalsh/Reuters)