An Afghan policeman carries a wounded man at the site of a suicide attack in Kabul March 25, 2015. Six people were killed and more than 30 injured in the suicide bombing in the Afghan capital on Wednesday that struck close to the presidential palace in the heart of the city, the Interior Ministry said. The suicide bomber had been travelling in a vehicle packed with explosives and it was not immediately clear what the target of the attack had been. (Photo by Omar Sobhani/Reuters)

Military vehicles surround a wreckage of a trolleybus, in Volgograd, Russia, Monday, December 30, 2013. A bomb blast tore through a trolleybus in the city of Volgograd on Monday morning, killing at least 10 people a day after a suicide bombing that killed at least 17 at the city's main railway station. Volgograd is about 650 kilometers (400 miles) northeast of Sochi, where the Olympics are to be held. (Photo by Denis Tyrin/AP Photo)

View of a light show on the city's iconic Arc de Triomphe monument during the New Year celebration in Paris, France, December 31, 2016. (Photo by Jacky Naegelen/Reuters)

Mounted cop in action on Tremont Street in Boston, Massachusetts, 1920 – 1929 (approximate). (Photo by Leslie Jones)

A policeman stands by a burning car, set alight during a communist march in the East End of London. (Photo by Topical Press Agency/Getty Images). Circa 1936

Attendants prepare to fill glasses for delegates before the opening session of the Chinese People's Political Consultative Conference at Beijing's Great Hall of the People, Thursday, March 3, 2016. The more than 2,000 members of China's top legislative advisory body convened their annual meeting Thursday, kicking off a political high season that will continue with the opening of the national congress on Saturday. (Photo by Mark Schiefelbein/AP Photo)

Harry Sprinkle eats a meal at St. John's Bread and Life, a free meal service, on December 23, 2011 in the Brooklyn borough of New York City. St. John's Bread and Life serves approximately 2,200 meals per day; the organization has existed since 1982. (Photo by Andrew Burton/Getty Images)

A car mechanic repairs a tire hoop at the Nicolini Collection Car Museum in Lima, Peru June 1, 2017. (Photo by Guadalupe Pardo/Reuters)