[ColdOne]

what is “Office of Special Investigations?”

[NCDragon]

It looks like an internal investigative branch of the Air Force:

FUNCTION

We are a federal law enforcement and investigative agency operating throughout the full spectrum of conflict, seamlessly within any domain; conducting criminal investigations and providing counterintelligence services.

http://www.osi.af.mil/main/welcome.asp

[Domangart]

The Office of Solved Investigations. They never take a case that isn't already solved.

[ExNewsExSpook]

Undercover investigative branch of the USAF; the Air Force equivalent of NCIS.

[Gen.Blather]

“what is “Office of Special Investigations?””

My sister was the first female agent in OSI. They handle any investigation that involves the Air Force; murder, suicide, fraud, espionage...If the Air Force is involved it’s their case. They frequently work with local law enforcement or other agencies when the jurisdictions intersect.