I have represented a number of people in investigations by an Office of Inspector General (or "OIG"). Many of my clients have been federal employees who were being looked at by the OIG for their agency. For federal employees in this situation, there really isn't very much information available about the process.
For that reason, I was curious to see online a pamphlet called "OIG Investigations and You." It's put out by the Office of Inspector General for the Corporation for National and Community Service (did you know there's a Corporation for National and Community Service, and that they have an Office of Inspector General? Well, now you do.)
I don't agree with everything in this pamphlet. For example, the pamphlet tells you that you shouldn't talk to others about if you've been interviewed by OIG agents because it might be obstruction of justice. I suppose that's true in an extreme case, but it seems to me more likely that it's a pain for OIG agents to not control all the information in an investigation and they'd like to scare people out of talking to, say, a lawyer hired to represent a target of an investigation.
That aside, it's actually a fairly decent starter document about what happens in an OIG investigation and what a federal employee's rights in an OIG investigation are.
If you have questions about how federal criminal charges are different than state criminal charges, please visit this page on Maryland federal criminal charges or Washington DC federal criminal charges.