The Open-Unsolved Unit of the Los Angeles Police Department's Robbery-Homicide Division, also known as the Cold Case Special Section, is a unit that "is responsible for reviewing Citywide 'cold case' homicides (five years since commission) and sexual assaults (two years since commission) to determine if additional investigation may be warranted as a result of scientific advances in DNA profiling, fingerprint comparison and/or ballistic testing. If this type of untested evidence is discovered or other information is developed indicating the crime may be solvable, RHD personnel assigned to the CCSS will investigate the crime."
Harry Bosch worked for the Open-Unsolved Unit from 2005 to 2006, partnering with his former colleague Kizmin Rider and closing the investigations into the deaths of Rebecca Verloren, June Wilkins, and Marie Gesto. He transferred back to the OUU again in November of 2010, and partnered with Detective David Chu from the Asian Gang Unit. During this time, he solved the murders of Lily Price and Anneke Jesperson.
Sometime after 2012, due to the crime rate decreasing, less cops were needed on the street, and as a result, the OUU was expanded to allow more police officers to work the large amount of cold cases. Many of the new officers were partnered with more experienced officers to gain experience. Bosch was partnered with Lucia Soto, and during this time they solved the murder of Orlando Merced.
The leadership of this unit changed hands every six months. Some of the lieutenants who have supervised this unit have been Abel Pratt, Gail Duvall, Cliff O'Toole, and Winslow Samuels.