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Police officers line the streets near the funeral of Officer Wenjian Liu in the Brooklyn borough of New York, Sunday, Jan. 4, 2015. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/Seth Wenig) ( APTOPIX NYPD Officers Shot )

NEW YORK, NY - JANUARY 04: Officers carry the casket of Police Officer Wenjian Liu from a funeral service at Aievoli Funeral Home in the Dyker Heights neighborhood on January 4, 2015 in the Brooklyn borough of New York City. Liu was killed with his partner Rafael Ramos on December 20, when the two were shot by Ismaaiyl Brinsley while sitting in their patrol car. (Photo by Eric Thayer/Getty Images) ( 461019528 )

New York City Mayor Bill de Blasio, center, walks with his wife Chirlane McCray, right, following funeral services for New York City police officer Wenjian Liu at Aievoli Funeral Home, Sunday, Jan. 4, 2015, in the Brooklyn borough of New York. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/Julio Cortez) ( NYPD Officers Shot )

A lone police officer stands front as other colleagues turn their backs while Mayor Bill de Blasio speaks during the funeral of New York Police Department Officer Wenjian Liu at Aievoli Funeral Home, Sunday, Jan. 4, 2015, in the Brooklyn borough of New York. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/John Minchillo) ( APTOPIX NYPD Officers Shot )

Some police officers turn their backs as Mayor Bill de Blasio speaks during the funeral of New York Police Department Officer Wenjian Liu at Aievoli Funeral Home, Sunday, Jan. 4, 2015, in the Brooklyn borough of New York. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/John Minchillo) ( APTOPIX NYPD Officers Shot )

A New York Police Department flag hangs from a FDNY ladder during the funeral of NYPD Officer Wenjian Liu at Aievoli Funeral Home, Sunday, Jan. 4, 2015, in the Brooklyn borough of New York. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/John Minchillo) ( NYPD Officers Shot )

CORRECTS VEHICLE IS NOT A HEARSE - The vehicle leading the funeral procession of New York Police Department Officer Wenjian Liu, seen in photo, passes along the funeral route as police officers salute, Sunday, Jan. 4, 2015, in the Brooklyn borough of New York. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/John Minchillo) ( CORRECTION NYPD Officers Shot )

Police helicopters do a fly over at the conclusion of the funeral service for slain New York City Police Officer Wenjian Liu January 4, 2015 in New York City. Officers Wenjian Liu and Rafael Ramos were killed in an ambush while sitting in their patrol car last month on December 20. Thousands of fellow officers, family, friends and current FBI director is James Comey are expected at the Brooklyn funeral home for the service. Officer Ramos, was buried last week in Queens. (Photo by Spencer Platt/Getty Images) ( 461020248 )

Mourners stand outside of Aievoli Funeral Home following funeral services for New York City police officer Wenjian Liu, Sunday, Jan. 4, 2015, in the Brooklyn borough of New York. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/Julio Cortez) ( NYPD Officers Shot )

Bystanders become emotional while listening to people speak during the funeral of Officer Wenjian Liu in the Brooklyn borough of New York, Sunday, Jan. 4, 2015. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/Seth Wenig) ( NYPD Officers Shot )

An FDNY firefighter salutes along the procession route during the funeral of New York Police Department Officer Wenjian Liu, Sunday, Jan. 4, 2015, in the Brooklyn borough of New York. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/John Minchillo) ( NYPD Officers Shot )

A spectator looks out onto officers during the funeral of New York Police Department Officer Wenjian Liu at Aievoli Funeral Home, Sunday, Jan. 4, 2015, in the Brooklyn borough of New York. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/John Minchillo) ( NYPD Officers Shot )

NEW YORK, NY - JANUARY 04: New York City Police Officers stand outside of a funeral service for New York City Police Officer Wenjian Liu at Aievoli Funeral Home at Aievoli Funeral Home in the Dyker Heights neighborhood on January 4, 2015 in the Brooklyn borough of New York City. Liu was killed with his partner Rafael Ramos on December 20, when the two were shot by Ismaaiyl Brinsley while sitting in their patrol car. (Photo by Eric Thayer/Getty Images) ( 461019582 )

A single police officer turns her back as Mayor Bill de Blasio speaks during the funeral of New York Police Department Officer Wenjian Liu at Aievoli Funeral Home, Sunday, Jan. 4, 2015, in the Brooklyn borough of New York. Liu and his partner, officer Rafael Ramos, were killed Dec. 20 as they sat in their patrol car on a Brooklyn street. The shooter, Ismaaiyl Brinsley, later killed himself. (AP Photo/John Minchillo) ( NYPD Officers Shot )