In a letter to U.S. Attorney Zachary Fardon and Cook County State’s Attorney Anita Alvarez, Chicago Mayor Rahm Emanuel has asked both Cook County and federal officials to investigate the racial slurs heard over Chicago Police Department radio frequencies.

A male voice was first heard on March 13th saying, “typical f—ing n—–,” during a conversation between 911 call center dispatchers and police officers.

To which a different male voice replied, “Find out what radio that comment came from.”

Then a female voice answers, “We don’t get radio numbers, but I’m already hollering for my supervisor.”

A male voice then says, “Black lives matter, my a—, f—ing n—–s.”

According to Mayor Emanuel, there have been three more instances of people broadcasting similar slurs over the police radio frequencies.

Authorities at the Chicago Police Department, which has been conducting an internal affairs investigation of the incidentswww, believe that the speaker in the transmissions is not a police officer or employee of the CPD.

“Subsequent investigation has indicated that the transmission was made by an unauthorized private citizen using non-city-issued equipment,” Emanuel wrote in his letter asking Fardon and Alvarez to investigate this as a hate crime, recalling that, “[a]lthough police frequencies are legally restricted to official use, the Chicago Police Department (“CPD”) and Office of Emergency Management and Communications (“OEMC”) have, at times, encountered private citizens who, with the aid of equipment that is publically available, make unauthorized transmissions o police radio frequencies.”

“The language used and the racial intolerance expressed do not represent the values of our police department or our city,” Emanuel wrote.

Activists, however, are not convinced that the messages came from outside of the department. Community leaders have called for the mayor to find and fire whoever made the racist transmissions.

Chicagoist notes that one Twitter user who regularly tracks police scanner claims that the original broadcast was made hours after the police were deployed to the Donald Trump rally which was eventually cancelled due to the risk of violence between supporters and protesters.