Chicago police are warning residents of a "polite" gunman who is wanted in more than 20 robberies over the last month. 

Police say the armed suspect has robbed more than 20 people on the North and West sides since the end of November, while typically "speaking in a polite manner."

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"On more than one occasion, he has signaled the cashier to keep quiet by placing his index finger to his lips," police said in the alert, the Chicago Sun-Times reported

He’s accused of typically approaching people from behind as they enter an apartment building, while pulling out a gun and taking their money, cell phones and jewelry, police say

Chicago police officers work at the scene near where two officers were shot at 63rd Street and Bell Avenue in Chicago on Aug. 7, 2021.

Chicago police officers work at the scene near where two officers were shot at 63rd Street and Bell Avenue in Chicago on Aug. 7, 2021. (Chris Sweda/Chicago Tribune/Tribune News Service via Getty Images) (Chris Sweda/Chicago Tribune/Tribune News Service via Getty Images)

He has also targeted convenience stores, liquor stores, a clothing store and a fast-food restaurant. He has sometimes entered a business while pulling out a gun, but fled before taking anything. 

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The suspect is described as Black, being somewhere between 5-foot-9 to 6-foot-2, and often wearing a black mask and hoodie. It’s also possible he has a neck tattoo, according to police. 

He was driving a silver Mitsubishi with Texas plates in the latest description of the suspect. Police say he often uses rental cars with out-of-state license plates. 

Сhicago, USA - July 11, 2012: Chicago police patch on the arm of an officer at the Taste of Chicago.

Сhicago, USA - July 11, 2012: Chicago police patch on the arm of an officer at the Taste of Chicago. ( iStock)

Crimes are currently plaguing the Windy City. Chicago police data shows there has been a 20% increase in theft crimes in the city from January to Dec. 19 of this year compared to the same time frame last year. Robbery crimes are about the same this year compared to last, sitting at 7,633 robberies as of Dec. 19 this year. 

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Murders are up 5% so far this year compared to last and criminal sexual assaults are up 29%. 

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Democratic Mayor Lori Lightfoot called on the federal government to assist with the increase in crimes, noting that she knows "people are scared." 

Chicago's Mayor Lori Lightfoot

Chicago's Mayor Lori Lightfoot speaks during a science initiative event at the University of Chicago in Chicago, Illinois, U.S. July 23, 2020. REUTERS/Kamil Krzaczynski (REUTERS/Kamil Krzaczynski)

She asked U.S. Attorney General Merrick Garland on Monday to send in agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives for six months to increase the number of gun investigations and gun seizures. 

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She said her goal is to "proactively and relentlessly bring peace to our city once and for all."