Guerra was the medical examiner of the GCPD. He frequently became frustrated by Edward Nygma, due to the latter doing his own autopsies on several bodies, including Coleman Lawson. Guerra begs Captain Sarah Essen to do something about Nygma's conduct, and when they next catch him with his hand inside a corpse, she suspends him. Guerra was later fired after being framed by Nygma, who broke into Guerra's locker and filled it with dismembered limbs.
He was then replaced by Leslie Thompkins.