JT Wicker was a crooked GCPD officer who acted as a mole for the Riddler during the events of Batman: Arkham Knight.
History
At some point, he came into contact and became an ally to the Riddler. Most of his jobs involved reporting to Riddler regarding whether Commissioner Gordon was picking up his trail, as well as leaving various Riddler Trophies across Bleake Island.
During the events of Scarecrow's threat against Gotham City, Batman deduced JT Wicker's ties to Riddler and interrogated him. Although he claimed Batman was going crazy with some guards agreeing, he eventually fessed up, which resulted in Batman throwing him into a cell, as well as implying that his association with Riddler meant he was no longer a cop.