Perverted Justice, founded by Xavier Von Erck in 2002, is best known for its role in NBC Dateline's "To Catch a Predator" television programs. These programs capture on camera the arrival of sexual predators at residential locations they have arranged with Perverted Justice volunteers for supposed sexual encounters. Supporters of Perverted Justice argue that it is a cost-effective means for law enforcement agencies to expand Internet monitoring and suspect-identification capabilities. Perverted Justice provides the computer equipment and hundreds of volunteer personnel hours that law enforcement agencies could not otherwise afford. Perverted Justice, working in cooperation with law enforcement agencies, contacts a law enforcement agency once a suspect crosses a specific and agreed-upon threshold that constitutes a law violation. The law enforcement agency assumes total control of the investigation from this point. Prospective volunteers undergo background checks and thorough training. All of their online work is monitored and recorded. Despite its record of working with police to arrest more than 157 suspected sexual predators, Perverted Justice has its critics, including some in law enforcement who prefer that police work be done only by professionals. For law enforcement agencies that prefer to use their own personnel in all phases of Internet investigations, Perverted Justice offers to train officers to perform the same functions as their volunteers.