In 2006, he announced his intention to run for the District Attorney's position when the sitting decided against running for reelection, and O'Shea was opposed by prosecutor and civil rights attorney Gabriel Williams.
In September of that year, O'Shea was assigned to lead the prosecution of serial killer Raynard Waits. Waits, known as the Echo Park Bagman, is being investigated for the murder of two women. O'Shea becomes involved in a proffer for Waits to admit to further murders, reveal the locations of the bodies and accept life imprisonment without parole in exchange for the prosecution ruling out the death penalty.
O'Shea arranges for Waits to take them to the burial site of one victim, Marie Gesto, which is in Beachwood Canyon. They are accompanied by Deputy Doolan from the Sherrif's department, several forensics technicians, Detective Harry Bosch (lead investigator on the Gesto case), Detective Kizmin Rider, Detective Freddy Olivas (lead investigator on the original two murders), Corvin (O'Shea's videographer) and Waits' attorney. O'Shea agrees that Waits can be uncuffed to climb a ladder across difficult terrain. Waits escapes while uncuffed, killing Olivas and Doolan and wounding Rider. O'Shea flees the scene initially and then returns when Waits has left. He then helps the survivors to transport Rider out of the woods.
In the aftermath of this incident an edited version of Corvin's recording is submitted to the police. O'Shea's flight and his discussions regarding uncuffing Waits have been deleted. O'Shea gives interviews to the media focusing on his actions in rescuing Rider in order to appear heroic. Bosch believes that O'Shea is responsible for editing the video to preserve his image. Furthermore, Bosch suspects O'Shea may have been involved in setting up Waits's false confession. He links O'Shea to the real culprit, Anthony Garland, through campaign contributions. O'Shea denies any involvement and then threatens Bosch's career, claiming that he has friends high up in the police department. Bosch is then threatened by the Officer Involved Shooting Unit and believes this is due to O'Shea's threats.
Bosch's ongoing investigation eventually reveals that O'Shea was not involved in Waits's phony confession and that he was being set-up through campaign contributions. O'Shea works with Bosch and the FBI to set up a sting in which Abel Pratt will gather evidence of Anthony's guilt in the Gesto murder and his father Thomas Garland's involvement in the conspiracy. Anthony shoots and kills Pratt and is then killed by the FBI. O'Shea is left to prosecute Thomas Garland.
O'Shea is played by guest star Steven Culp in the 2015 streaming series Bosch. He is a recurring character in the first, second, third and fourth seasons. O'Shea's involvement in the Raynard Waits case is similar in the series, including his culpability for Waits' escape from custody.