Which PSI is conducted on personnel who require TOP SECRET and critical SAP Information?

The Single Scope Background Investigation (SSBI) is the correct answer because it is the comprehensive investigative process mandated for individuals seeking access to sensitive classified information, particularly at the TOP SECRET level. This investigation gathers extensive data about the individual’s background, including personal history, employment records, and character references, covering various aspects of the person’s life over an extended period. The SSBI is specifically designed to assess the individual's loyalty, reliability, and trustworthiness when handling sensitive information, such as critically sensitive Special Access Program (SAP) data.

In contrast, the other options represent different types of checks that might be applied under different circumstances but do not meet the depth of inquiry required for TOP SECRET access. For example, the National Agency Check is a more limited check primarily focusing on criminal history, while the Access National Agency Check with Inquiries includes additional inquiries, it is still not as thorough as the SSBI. Similarly, the National Agency Check with Local Agency and Credit Checks is intended to provide information on local law enforcement and credit history but lacks the comprehensive background scope of the SSBI. Therefore, for accessing TOP SECRET and critical SAP information, the Single Scope Background Investigation is the appropriate choice due to its detailed nature and thoroughness.