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 dead body is seen on the ground after violence erupted in the Independence Square in Kiev February 20, 2014. Ukrainian protesters seized back Kiev's Independence Square in fresh clashes with riot police on Thursday that left several injured and possibly two demonstrators dead. (Photo by David Mdzinarishvili/Reuters)

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)

A woman walk by South Korean police during a anti-terror exercise on March 9, 2012 in Seoul, South Korea. The drill is part of South Korea's preparation for the upcoming 2012 Seoul Nuclear Security Summit, scheduled for March 26 and 27. Some 50 world leaders, including U.S. President Barack Obama, are expected to attend the summit to discuss how to make the world safe without nuclear weapons. (Photo by Chung Sung-Jun/Getty Images)

A police officer fires his tear gas launcher during a clash with student protesters in Surabaya, East Java, Indonesia, Thursday, October 8, 2020. Thousands of enraged students and workers staged rallies across Indonesia on Thursday in opposition to the new law they say will cripple labor rights and harm the environment. (Photo by Trisnadi/AP Photo)

Polish police in riot gear detain protesters, angry over new restrictions aimed at fighting the coronavirus pandemic, in Warsaw, Poland, Saturday, October 24, 2020. The protesters included entrepreneurs, far-right politicians, football fans and vaccine opponents. The clashes come amid rising social tensions and as new restrictions just short of a full lockdown took effect Saturday. (Photo by Czarek Sokolowski/AP Photo)

A police officer patrols as people party on a street as pubs shut for the night due to tier 3 restrictions in Soho, as the spread of the coronavirus disease (COVID-19) continues in London, Britain, December 15, 2020. (Photo by Henry Nicholls/Reuters)