If you found out your Leader or Immediate Supervisor was doing something against the law, like fraud, what would you do?

Not this situation but I flunked a Foreign Officer in my class because I caught him cheating on a test. My E-8 said pass him. I said no. I don't pass cheaters. So off we go to my Captain. It was explained to me that this can and most likely cause an incident. I told my Captain I don't care I caught him cheating on a test and I cannot and will not pass him. My Captain smiled and dismissed me. Someone changed his grade but not me.

Start figuring who was not involved and could help me report it

Ale it up the chain, if I had proof, and I told my PSG and 1SG.

I was a Reserve SNCO on a EAD tour. I was assigned to a RegAF base and unit, one that had high visibility (the Secretary of the Air Force regularly visited). An O-3 back at my parent unit sent out "questionable pictures" of scantily clad young ladies over an offical email group I was part of. This violated all sorts of regs not to metion it could be construed as Conduct Unbecomming An Officer (CUBO). When the ax fell I wanted no part of what was comming so I emailed the officer in question. I politely but very explicitly pointed out the illegal nature of what he was doing. I respectfully requested that he no longer include me on any future emails containing such contents. I BCC my direct report (a RegAF CMSgt holding the title Commandant). When things went sideways and I was interviewed I had documented proof that I was not a party to these events, that I had reported them to my superiors, and that I had warned the O-3 to cease his illegal acts. I walked; the O-3 didn't.

I am amazed that someone would even ask such a thing. If my supervisor was robbing a bank, committing murder, or molesting children???????
Here is a thought stop them in the act, report him, tell someone, if your not in a position to stop it get someone who is. Do the right thing!
I'm not saying flag down a cop if you think someone is speeding, If someone is seriously committing a crime and you know it, you have a moral and ethical obligation to DO THE RIGHT THING.

Would have no choice but to report them.

The only thing I saw was something called "Basket Leave". The request chit for leave would go to personnel and be thrown into the "in" basket. The requester went on leave and when he returned his leave wouldn't be recorded on his pay file and the chit would disappear. I caught on when a coworker seemed to be going on leave to much to me. I said something about it seemed as if he'd just had leave and he explained it t me. The guys in personnel did it for their friends.

"Oh, what a tangled web we weave" = ok...

What does this say about you, if you don't say anything about it?

I have always made decisions based on certain criteria. (1) Does the situation/activity violate what would be considered ETHICAL? (2) Does the situation/activity violate what would be considered MORAL? and lastly (3) Does the situation/activity violate any LAW, Regulation, SOP, Policy, or Procedure ???

If the answer is YES,YES,YES...then I would have a decision to make...If it was something petty (Let's say a 10 dollar error on a Travel Voucher) then I would confront the individual, If it was egregious, (Let's say a 10 Million Dollar re-routing of funds to a personal account) then I would report it through proper channels.

FRAUD regardless of the amount, violates all three criteria (ie) Contract kickbacks, a clear violation of the Federal Acquisition Regulation.

We don't live in a courtroom... A whistleblower can put themselves in considerable danger depending on the circumstances. Proper evidence would need to be gathered and the whistleblower's statement verified and fact-checked. The whistleblower would need to be protected. I remember in one situation a Soldier was emergency PCS'd to a new duty station overseas while the court case was going on. Later, the other Soldier involved was court-martialed under chapter 10, found guilty, Dishonorably Discharged, and incarcerated.

She was my Fort Riley Psychologist.
https://abc7ny.com/archive/7932052/

We were told to bury aircraft, tanks, munitions, armor, scud missiles in one foot of dirt before pushing out of Kirkuk Iraq. Incinerator crew from COS warrior were mad to find a scud missile in the trash cans. Oh, great Iraq pull out of 2011 was a shit fest on parade rest. Everything had to go somewhere man, pushing equipment or comes containers into a 1-foot hole. With one soldier at a time per conex does that. So many DOD laptops and computers just laying around when we left. Passwords written on the monitors by orders of E-7 to E-9s forgetfulness paid out I guess. Anyone here seen ISIS videos with our gear, tanks, helicopters, and 155mm cannons on Youtube in 2012-2021? Knows what I mean, by orders of Obama leave Iraq in 2011 alone as it is, gear intact. Everyone knows about the Kirkuk Iraq scud missiles in the dumpsters and incinerator incinerator incidents. All 100% of my command spent, while 2011 great pull out of Iraq, planning their next unit move or transfer or promotion out of the First ID. As a private, all my OIG reports came back with a huge saying every time, said fuck you! I never gained so much weight in my life to leave Fort Riley in a hurry as weight gain discharge. Must have been billions of dollars and security issues into the trillions of dollars left for ISIS. John McCain also said Fuck You to all my reports to him. Saying we have our hands busy already with ISIS in 2013. I left three months on weight gain discharge after my deployment on purpose before my MED Board review even kicked in. I told generals to OIG, every time they said quoted, 'You want to end up in Leavenworth or worse soldier'! This was from the great 2011 Iraq pull out of the gulf war ending. Lucky