This November 27, 2007 memo justifies the future use of contractors as High Value Detainee Interrogators (HVDI). The memo states that before September 11, 2001 the CIA had no resident expertise in interrogation and therefore contract interrogators, who operate under the authority and direction of senior Agency staff officers, have been a "key component" in the CIA's Global War on Terrorism. The memo argues that it was not feasible for the CIA to create a group of long-term experienced interrogators because it takes years to develop these skills and staff officers change assignments every couple years. As a result, the CIA decided to end the training to use CIA staff officers as interrogators.