Mass. Bay Transportation Authority Police Chief William J. Bratton, left, answers questions at a news conference at the McCormack Building in Boston on Wednesday, July 20, 1983. (AP Photo)
Bill Bratton, chief of the New York Transit Police, talks to a homeless man in New York, Nov. 21, 1991, on a routine tour of the New York City subway system. (AP Photo/Betsy Herzog)
(AP Photo/Richard Drew)
Police Commissioner William Bratton speaks at a news conference May 9, 1994, in New York. (AP Photo/Luc Novovitch)
New York City Mayor Rudolph Giuliani, right, and Police Commissioner William Bratton, left, face reporters during a news conference on Friday, May 19, 1995 in Police headquarters. (AP Photo/Clark Jones)
Police Commissioner William Bratton, center, shares a laugh with New York Mayor Rudolph Giuliani, left, during a news conference Tuesday, March 26, 1996 at City Hall in New York. (AP Photo/Richard Drew)
Los Angeles Police Chief William Bratton quotes from a book about racial profiling, during the announcement of the first posting of data collected by the LAPD Jan. 6, 2003. (AP Photo/Chris Carlson)
Los Angeles Police Chief William Bratton speaks during a meeting of the Board of Police Commissioners Tuesday, July 13, 2004, in Los Angeles. (AP Photo/Nick Ut)
In this Tuesday, Jan. 31, 2006 file photo, former Los Angeles Police Chief William Bratton, left, speaks as then Los Angeles Police Commission president John Mack listens. (AP Photo/Nick Ut)
Los Angeles police Chief William J. Bratton holds the department's media guideline during a news conference with city leaders at Los Angeles City Hall Wednesday, May 2, 2007. (AP Photo/Kevork Djansezian)
Los Angeles Police Chief William Bratton discusses issues related to the clash between LAPD officers and demonstrators, journalists and others on Friday, May 4, 2007. (AP Photo/Reed Saxon)
Los Angeles Mayor Antonio Villaraigosa, left, listens as Police Chief William Bratton, center, speaks to reporters after a man had barricaded himself in a house Feb. 7, 2008. (AP Photo/Reed Saxon)
Outgoing Los Angeles Police Chief William Bratton hands in his badge as he prepares to leave at an "End Of Watch" ceremony, at police headquarters in Los Angeles Oct. 28, 2009. (AP Photo/Reed Saxon)
In this Aug. 6, 2009 file photo, William Bratton, then head of the Los Angeles police department, speaks at a new conference in Los Angeles. (AP Photo/Philip Scott Andrews)
USC President, Steven Sample, left, presents an honorary degree in law to former LA Police Department Chief, William Bratton, at the University of Southern California May 14, 2010. (AP Photo/Damian Dovarganes)
Chef Nobu Matsuhisa, right, and former LAPD Police Chief William Bratton at the FIJI Water Kitchen during the "Silver Spoons: 25 Years of Chefs & Celebrations" event June 14, 2010. (Diane Bondareff/AP Images for FIJI Water)
Former Los Angeles Police Chief William Bratton, center, who is hired as a security consultant for the Los Angles Dodgers, speaks during a news conference April 14, 2011. (AP Photo/Jae C. Hong)
Rev. Al Sharpton sits between newly-named New York police commissioner William Bratton, left, and Mayor-elect Bill de Blasio, right, on Saturday, Dec. 7, 2013. (AP Photo/John Minchillo)
NYC Mayor-elect Bill de Blasio, left, and newly-named police commissioner William Bratton, center right, speak following a tribute to Nelson Mandela Dec. 7, 2013. (AP Photo/John Minchillo)
NYC Mayor Bill de Blasio, right, and police commissioner Bill Bratton, center, present an award to a recruit during a NY Police Academy graduation ceremony, Monday, Dec. 29, 2014. (AP Photo/John Minchillo)
NYPD Commissioner Bill Bratton, his wife and other officials arrive at the wake of NYPD Officer Wenjian Liu at Aievoli Funeral Home, Saturday, Jan. 3, 2015, in Brooklyn. (AP Photo/John Minchillo)
Bill Bratton and Rikki Klieman attend the 2015 White House Correspondents' Association Dinner at the Washington Hilton Hotel on Saturday, April 25, 2015, in Washington. (Photo by Charles Sykes/Invision/AP)
New York City Police Commissioner Bill Bratton greets Brian Moore's family members while waiting with police officers outside of Jamaica Hospital in New York, Monday, May 4, 2015. (AP Photo/Seth Wenig)
NYPD Commissioner Bill Bratton, left, presents Savannah Solis, of Tyler, Texas, a gift during a news conference at New York City police headquarters, Wednesday, Feb. 25, 2015. (AP Photo/Mary Altaffer)
(AP Photo/Richard Drew)
NYPD Commissioner Bill Bratton, with New York City Mayor Bill de Blasio, right, and NYPD Chief of Department James O'Neill, left, speaks during a press conference June 10, 2015. (AP Photo/Kevin Hagen)
New York Police commissioner William Bratton arrives for the funeral service of Officer Randolph Holder, Wednesday, Oct. 28, 2015, in New York. (AP Photo/Julie Jacobson)
New York Police Department Commissioner William Bratton, center, walks to the scene of a fatal shooting, Monday, Nov. 9, 2015, in New York. (AP Photo/Mark Lennihan)
New York City Police Commissioner William Bratton listens during a news conference as preparations for the Macy's Thanksgiving Day Parade continue Wednesday, Nov. 25, 2015. (AP Photo/Frank Franklin II)
Officer Sherrod Stuart, center, poses with New York City Police Commissioner William Bratton, left, Saturday, Jan. 9, 2016, in New York. (NYPD via AP)
New York City Police Commissioner William Bratton speaks to the media after the NYPD crushed about 70 confiscated motorcycles and all-terrain vehicles Tuesday, May 17, 2016. (AP Photo/Kathy Willens)
Jan. 12, 2016 file photo, New York City Police Commissioner William Bratton, left, speaks during a news conference in New York's City Hall, as New York Mayor Bill de Blasio listens (AP Photo/Richard Drew)
In this Jan. 12, 2015, file photo, New York City Police Commissioner William Bratton speaks during a news conference at police headquarters in New York. (AP Photo/Richard Drew)