Colombian police help carry people's household belongings across the Tachira River from Venezuela, top, to Colombia, on the border that separates San Antonio del Tachira, Venezuela from Villa del Rosario, Colombia, Tuesday, August 25, 2015, during a mass exodus of Colombians. Venezuelan President Nicolas Maduro vowed to extend a crackdown on illegal migrants from neighboring Colombia he blames for rampant crime and widespread shortages, while authorities across the border struggled to attend to droves of returning deportees. (Photo by Eliecer Mantilla/AP Photo)

A protester uses molotov cocktails against riot police during May Day protests on May 1, 2010 in Athens, Greece. (Photo by Milos Bicanski /Getty Images)

Riot police walk in the street as a couple kiss on June 15, 2011 in Vancouver, Canada. Vancouver broke out in riots after their hockey team the Vancouver Canucks lost in Game Seven of the Stanley Cup Finals. (Photo by Rich Lam/Getty Images)

Police academy graduates march during their graduation ceremony in Islamabad, Pakistan May 18, 2015. Out of the 408 graduating officers, 76 female officers were inducted into the Pakistan police force, according to the police force. (Photo by Caren Firouz/Reuters)

People crowd together in an attempt to buy chickens at a Mega-Mercal, a subsidized state-run street market, in Caracas January 24, 2015. President Nicolas Maduro shook up complex currency controls on Wednesday and also prepared Venezuelans for a rise in the world's cheapest fuel prices in response to a recession worsened by plunging oil revenue. The socialist-run OPEC member's economy shrank 2.8 percent in 2014 while inflation topped 64 percent, the socialist leader announced in a speech to parliament, in what is almost certainly the worst performance in Latin America. (Photo by Carlos Garcia Rawlins/Reuters)

A student aims a stick of wood at Bolivarian National Police officers during clashes outside the Central University in Caracas, Venezuela, Thursday, June 9, 2016. Students had planned to march from Venezuela's top university to elections headquarters, but hundreds of police in riot gear blocked the way. Students covered their faces with Venezuelan flags and threw bottles, stones and sticks while police lobbed tear gas. (Photo by Fernando Llano/AP Photo)

Afghan police recruits undergo training at the Afghan Police Academy October 5, 2010 in Kabul, Afghanistan. (Photo by Majid Saeedi/Getty Images)

Metropolitan Police officers prepare to carry out a raid on a property on the Churchill Gardens estate in Pimlico during Operation Woodstock on August 11, 2011 in London, England. Over 1,000 people have been arrested since the rioting began on Saturday and Police have started to raid properties across the capital as they round up people suspected of involvement in the rioting and recover stolen property. (Photo by Anthony Devlin - WPA Pool/Getty Images)