for the required demonstration. For example, the FBI could easily meet the threshold Exemption 7 burden for a document that gives guidelines for searches incident to arrest because its general law enforcement duties routinely involve such searches. But it would be more difficult to prove, and require greater evidence to demonstrate, a nexus between an FBI investigation into a “highly controversial figure in California education” whom the FBI was attempting to have removed from office and “a plausible law enforcement purpose.” Rosenfeld, 57 F.3d at 809. And, for some records, it may be impossible to prove a rational nexus to valid law enforcement purposes. This approach is similar to that of the District of Columbia Circuit. When considering investigatory materials, that court r . 2007) (<HOLDING>); PHE, Inc. v. Deft of Justice, 983 F.2d 248,
holding that records concerning polygraph examination procedures and other law enforcement techniques are protected from disclosure under  exemption 7e holding that computer transaction and function codes that reveal how to navigate and retrieve information from a law enforcement database were properly withheld under exemption 7e holding that requests for metadata and database schema of law enforcement information databases qualify for exemption under 7e holding that numerical codes used to identify information and individuals as well as codes related to procedures concerning the use of law enforcement resources and databases  and case program and access codes were properly withheld under exemption 7e holding cia clearance and investigatory processes and related law enforcement techniques and procedures exempt under exemption 7e