Details are provided on NIJ’s technical assistance, training, and grant resources that have continued to promote a culture of cooperation among law enforcement agencies at the local, state, and federal levels. Up until just over half of the 1900s, U.S. police departments operated in relative isolation from each other and from federal law enforcement agencies. In the 1970s and 1980s, however, the need for interagency cooperation became evident as new types and patterns of violent crime emerged across jurisdictions. By the later 1970s, a series of brutal sexual serial killings across jurisdictions caused widespread public concern and challenges for law enforcement. This prompted NIJ to support a pioneering FBI initiative that focused on unsolved and cross-jurisdictional sexual serial killers. With NIJ grant awards, the FBI developed scientifically based methods for the criminal profiling of sexual murderers. One outcome was the development of a new data set of serial-killer characteristics derived from crime-scene evidence. In addition to the data-based linking of sexual serial killings, a nationwide spike in missing persons was also occurring, with no known crime scenes. Law enforcement investigative efforts lacked the means and precedents to mine critical, connecting evidence beyond jurisdictional borders, which hampered the linking of case characteristics. NIJ’s commitment to forging a more coordinated and resourceful response to complex, multi-state crimes led to the selection of the FBI as the logical agency for housing and managing a new, computer-based violent-crime data repository and investigative center. This enabled local law enforcement agencies to access shared data on violent crime, along with expert advice and analysis.