A day after killing an unarmed man, an unidentified Chicago Police Department (CPD) officer has been suspended.

The officer shot and killed Jose Nieves, 39, on Monday (January 2). Chicago Tribune reports that the 57-year-old officer works on the city’s transit detail and that he not only knew Nieves, but had recently argued with him. He was off duty at the time of the shooting.

During a statement issued yesterday (January 3), police spokesman Anthony Guglielmi said that the paid punishment is the “strongest step a department can take” during an open investigation. CPD and the Independent Police Review Authority are conducting parallel investigations.

“I have a lot more questions than I have answers at this time,” police superintendent Eddie Johnson told the press on Monday at the scene of the shooting.