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)

Enya Kim from the Natural History department at auctioneers Bonhams & Butterfields stands in front of one of the world's largest set of shark jaws comprised of about 180 fossil teeth from the prehistoric species, Carcharocles megalodon, which grew to the size of a school bus, at the Venetian Resort Hotel Casino September 30, 2009 in Las Vegas, Nevada. (Photo by Ethan Miller/Getty Images)

Swiss police officers stand beside of mock gates of the NEAT Gotthard Base Tunnel inside the event hall for the upcoming opening ceremony near the town of Erstfeld, Switzerland May 31, 2016. The celebrations of the opening of the Gotthard Base Tunnel will start on June 1, 2016. With a length of 57 km (35 miles) crossing the Alps, the Gotthard Base tunnel is the world's longest train tunnel. (Photo by Arnd Wiegmann/Reuters)

People carry lychee for sale on a motorbike on a street in Luc Ngan, Bac Giang province, Vietnam, 22 June 2016. Lychee output in Bac Giang province is expected to reach 130,000 tonnes this year. China is still Vietnam's main lychee export market so far, buying around 60 percent of the annual crop, according to official reports. (Photo by Luong Thai Linh/EPA)

A labourer carries a basket of bananas inside a wholesale fruit and vegetable market in Bengaluru, India, August 22, 2016. (Photo by Abhishek N. Chinnappa/Reuters)

A portrait of French WWI soldier Edouard Marius Ivaldi is displayed on a tablet, in this illustration picture, alongside his battlefield grave memorial, a wooden cross with a battlefield helmet in Champagne, eastern France, November 3, 2015. (Photo by Charles Platiau/Reuters)

In this Sunday, June 17, 2018, file photo, an Indonesian resident walks past graffiti on a downtown street in Hong Kong. There are 370,000 foreign domestic helpers in the Chinese territory and about 49.4 percent from Indonesia. (Photo by Vincent Yu/AP Photo)

A woman touches a robot at the 2018 World Robot Conference in Beijing on August 15, 2018. The conference will be held from 15 to 19 August and will include a conference on robotics, an exhibition and a robot competition with the participation of robotics enterprises to showcase their robot products. (Photo by Wang Zhao/AFP Photo)