However, the law of most states do provide a qualified immunity for reports of possible criminal wrongdoing to law enforcement. I don’t see this as a huge problem here. Moreover, truth is always a defense to a defamation claim, so if he sticks to the facts he’s uncovered, there’d be nothing for the state employees to pursue.
I used to be a government employee myself, but for the federal government. I will tell you that at least in the agency in which I worked, improper travel claims were a big deal and employees who had a habit of submitting bad claims were at the very least fired and several that I knew of were prosecuted for it. One of those employees was close to retirement and as a result of his conviction he lost his pension, a very devastating result for him. A key factor in the cases referred to prosecution is that the evidence was quite clear that these employees were actually falsifying the data — they were clearly proven to have claimed expenses they never incurred. It’s a harder problem to convict for expenses that were actually incurred by the employee but the item involved is not one that is eligible for reimbursement. There, unless the employee tried to disguise the expense as something that was covered it would not likely be a criminal problem. Nevertheless, when I was a manager approving those expenses I cautioned employees that one of the fastest tickets to unemployment and possible prison in our job was messing around with the travel reimbursement.
Whether the OK state government and the DA would take a similar dim view of improper travel reimbursements I cannot say. Each state and the federal government are different. The exact facts of each reimbursement claim matter, too, of course.