Protester Lauren Digioia wears police tape during an Occupy Wall Street protest in Union Square on March 19, 2012 in New York City. Protesters affiliated with the movement are gathering in Union Square today following 73 arrests at a six-month anniversary rally at Zuccotti Park over the weekend. (Photo by Mario Tama/Getty Images)

This combination of April 15, 2013 and April 2, 2014 photos show a police officer clearing Boylston Street following a bomb blast near the finish line of the 2013 Boston Marathon, and pedestrians crossing at the same corner nearly a year later in Boston. (Photo by Charles Krupa/AP Photo)

A Carlsbad,Calif. police officer turns traffic away as flames leap behind him Wednesday, May 14, 2014, in Carlsbad, Calif. Weather conditions that at least temporarily calmed allowed firefighters to gain ground early Wednesday on a pair of wildfires that forced thousands of residents to leave their homes. (Photo by AP Photo)

A model of a prehistoric icthyosaurus is dragged from its pond in the grounds of Crystal Palace, London, for its annual clean. The 'keeper' is being helped by some of the local police force. (Photo by Fox Photos/Getty Images). February 1927

Workers feed water to a Slow Loris at the Guangdong Wild Animal Rescue Centre on December 21, 2004 in Guangzhou, China. Many protected species at the Centre have been seized by Police from illegal traders. (Photo by China Photos/Getty Images)

A man carries a smoke flare as far-right activists march during the Gay Pride parade on June 12, 2016 in Kiev. More than 700 gay rights activists marched through central Kiev on June 12 amid a massive police presence for the third such gay pride event in the ex-Soviet country where homophobia remains widespread. The June 12 march was the first ever gay pride rally to be held in central Kiev, prompting an unprecedented security operation with several thousand police and National Guard officers lining the route during the event, which lasted around 20 minutes. (Photo by Yuriy Kirnichny/AFP Photo)

A member of the German wireless police picks up signals on the radio equipment he carries on his back, while his colleague takes notes. (Photo by General Photographic Agency/Getty Images). Circa 1925

Two children jumping through a water hydrant's shower on a New York street. They have come from a neighbouring co-educational playgroup organised by the city's Police Department. (Photo by Orlando/Getty Images). 1950