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)

The sun rises over the River Brue on the Somerset Levels as temperatures in parts of the south west drop below freezing, on January, 20, 2015. (Photo by Ben Birchall/PA Wire)

Fans dressed up in costume await the cast members on the red carpet at the world premiere of the film "The Avengers: Endgame" in Los Angeles, California, April 22, 2019. (Photo by Mario Anzuoni/Reuters)

A Guarani Mbya man smokes a pipe next to a cut tree as he occupies land as a protest against real estate developer Tenda which plans to build apartment buildings here, next to his indigenous community's land in Sao Paulo, Brazil, Thursday, February 6, 2020. In response to an injunction filed by the builder, a judge has authorized the eviction of the indigenous protesters from the builder's property. (Photo by Andre Penner/AP Photo)

Women walk on a sidewalk in northern Tehran, Iran, Thursday, January 9, 2020. (Photo by Vahid Salemi/AP Photo)

In this aerial photo taken on March 28, 2019 a hot air balloon flies over Putrajaya during the international hot air balloon festival in Putrajaya, Malaysia. (Photo by Mohd Rasfan/AFP Photo)

Members of the British Thai celebrate the Thai New Year (Songkran) at the Buddhapadipa Temple on April 16, 2018 in London, England. Buddhapadipa Temple, the largest Thai temple in the UK with religious ceremonies Thai classical music and dancing performances as well as stalls selling Thai food, groceries and souvenirs. (Photo by Paul Quezada-Neiman/Alamy Live News)

Charlotte Caslick of Australia is tackled by Jasmine Joyce of Wales during the Rugby Sevens Women's Pool B match between Australia and Wales on day nine of the Gold Coast 2018 Commonwealth Games at Robina Stadium on April 13, 2018 on the Gold Coast, Australia. (Photo by Dan Mullan/Getty Images)