To protect the welfare of the American people, all people who work for the United States government must be reliable, trustworthy, of good conduct and character, and of complete and unswerving loyalty to the United States. Federal employees, contractors, and military members must undergo a background investigation. The extent of the investigation will depend on the type of job and the degree of harm the person in that job could cause. Even if a job does not require a security clearance to access classified national security information, regulations require an investigation for a suitability determination.
The sponsoring (employing or hiring) agency initiating your investigation determines the appropriate level of investigation. If they're an authorized Investigations Service Provider (ISP), they may conduct the investigation themselves. If they're not, they may ask another ISP, like DCSA, to conduct the investigation.