MILWAUKEE (CBS 58) -- The Milwaukee Police Department says one of their officers was arrested Wednesday, March 12, following "significant allegations of criminal misconduct."

He's accused of helping a convicted felon commit crimes and lying to federal investigators.

MPD says the officer-identified as Juwon Madlock- resigned from the department at the time of his arrest, after nearly 10 years of service. 

According to a criminal complaint, officers arrested a different man, and while searching his phone, they found conversations with Officer Madlock, talking about a range of crimes they were involved in together. 

Investigators are accusing Madlock of transferring ammunition to a felon, possession of a machine gun, lying to federal agents, obstruction, and selling or receiving stolen goods. 

In a statement Friday, the police department said, in part, "Milwaukee Police Chief Jeffrey Norman expects all members, sworn and civilian, to demonstrate the highest ethical standards in the performance of their duties and was extremely disappointed to learn about the misconduct in this case."

An investigation led by the FBI is open and ongoing.

MPD says they are acting in full cooperation.