CHICAGO (Reuters) - The number of homicides in Chicago increased 76 percent in January compared to last year as Mayor Rahm Emanuel’s approval rating slumped to a record low in the aftermath of the release of a video showing a white police officer killing a black teen.

Chicago Mayor Rahm Emanuel (C) participates in a panel discussion on Reducing Violence and Strengthening Policy and Community Trust at the U.S. Conference of Mayors in Washington January 20, 2016. REUTERS/Gary Cameron

The nation’s third-largest city usually sees more violence in the summer months but 51 homicides were reported this January, up from 29 in 2015. It was the most January homicides since 2000, according to a Chicago Tribune analysis of police statistics.

The total number of shooting victims in the city in January more than doubled to 292, compared to January 2015.

The Chicago police said in a statement on Monday that the spike in shootings has been driven by gang conflicts and “retaliatory violence” and that the vast majority of incidents originated from “petty disagreements.”

Also on Monday, the Tribune released a poll that found Emanuel’s job approval rating has dropped to 27 percent, the lowest in his administration. This is a drop from 52 percent in late March 2015, before his April re-election.

The poll of 985 city voters conducted Jan. 20 to 28 had an error rate of plus or minus 3.2 percent.

Three out of four voters said they did not believe Emanuel’s statements about the October 2014 fatal police shooting of Laquan McDonald, 17. Emanuel has said he had not seen the video of Officer Jason Van Dyke shooting McDonald 16 times before the city approved a $5 million settlement to McDonald’s family.

The video was released on Nov. 24, 2015, the same day Van Dyke was charged with murder. Protesters have said officials took too long to charge Van Dyke and release the video, and have called for Emanuel’s resignation.

In response to the crime increase, Chicago police said that they moved more than 350 police officers and 31 sergeants from foot patrol into vehicles to increase their visibility and mobility, along with conducting targeted raids in problematic areas.

The reduction in foot patrols is a reversal of past tactics. In 2013, Chicago police touted the expansion of foot patrols in the city’s most dangerous neighborhoods.

The U.S. Justice Department is investigating the department’s use of deadly force. Use of force by law enforcement has been the focus of national debate since a series of high-profile fatal shootings of minorities by mainly white police officers.