Dtjytyk

He literally had someone else take the exams for him

If you wanted to speak out, that was really the right time, not so many years later when damage is done and every accusation is virtually unprovable.

His doctoral thesis was weak and the defense round wasn't difficult.

There are many weak PhD theses around, and it's up to the universities and to the defense committees to decide which level of weakness is acceptable before rejecting a candidate (gosh, if we were to object to any "weak" degree...).

Do I tell his employer? Do I tell the university? Do I let it go?

You let it go because, as you said, you've nothing to prove your accusations (and the university would have no interest in undertaking an investigation after such a long time without any evidence to start with). And he is now in industry, and it's up to his employer to decide whether to promote or demote him according to his work performance and to decide whether the PhD title is just a vacuous document in his hands.

Different is the case where, for instance, you can prove that a student cheated by plagiarising other works. Here, there is evidence that can be used to revoke a degree, as it happened in some cases.

You should stop beating the horse, because it is dead now. You had a chance but you lost it when you were in school and when something could have done about it. Right now, I believe you don't have any option other than letting it go. I can imagine your frustation in seeing him moving up the ladder (probably higher than you). If you didn't say anything when it actually could have changed anything, you should make peace with it now.

Even if you tell his employer now, what proof do you have to prove your allegation? University probably won't have any interest in pursuing this now. Honestly speaking, I sense jealousy in your post that he is doing good after all this. What you call "schmooze king", is actually a desirable skill in industry. More connections you can make, better are your chances to move up the ladder faster. So I would say, stop being obsessive with his success (with fraud or otherwise), and focus on your career.

Relax. His cheating has earned him nothing except a worthless piece of paper. He knows he doesn't have the skills to do scientific research, and most likely his employer has worked it out too.

All he's done is waste a number of years when he could have been climbing the corporate sales ladder. Someone with those smoozing skills and lack of ethics could have started as a commission-based shop assistant, moved to used cars or real-estate and then a big corporate sales department, or even politics. He'd be a lot richer and more senior if he'd concentrated on the things he was good at.

I wouldn't even worry about his clients. No one expects a salesman to be particularly knowledgeable in their field (or they'd be in research or operations rather than sales) or to be particularly honest.

Be happy that he's found a job that suits him, and for all the research scientists who don't have to work with him.

I agree with others generally regarding your specific question about telling the school(s). You missed your chance to really stop him when you should have, at least if you cared about him not getting undeserved degrees.

However I strongly disagree with some of these "let it go" answers, at least in terms of their lack of concern. An unqualified chemist who doesn't know the fundamentals (that their resume claims they know) can literally kill people. Stories abound of such idiots in chemistry-related industries. As for the answer extolling "hard work". A person who worked hard to be a fraud sounds like a more dangerous type of fraud to me.

A pharmaceutical rep shouldn't be in a position to do any damage, if everyone else does their job properly. But with those credentials he is especially dangerous as people might be more trusting of a phd's claims. And let's not forget this is a guy who doesn't care about silly things like "rules" or doing things the right way.

Your concern needs to be about the damage he can do now. And the people who would care about that are his employer. However this is beyond the scope of this forum and I really don't have an answer how to address that. It is much more specific and legal question to your situation. Generally, others are probably right that there's not much you can do at this point from afar.

I have no way to prove anything. I'm sure none of those guys that took his tests for him will come forward and tell the truth. He has gotten away with fraud.

If you have no evidence of wrongdoing then, even if you decided to do something, there is really not much you could legitimately do. Allegations of the type you are making are serious, and would require evidence. If you are confident that you would not be able to obtain corroborating evidence of your assertions, then there is really no reasonable prospect of any successful action against this person. So yes, in the absence of any evidence of the asserted wrongdoing, he has gotten away with it.

As to the possibility of telling his employer, if you make adverse allegations in this way, and they cause this person employment damage, this could potentially give rise to a legal action against you for defamation. There is a "defence of truth" in such actions, but this requires to person making allegations to prove these on the balance of probabilities. If you are considering doing this you should first seek legal advice.

I mean there is nothing actionable you have now, but this dude clearly doesn't care about rules, and I'm sure he cheats in some capacity again, so you catch him in his most recent round of cheating (seems like a lot of work) or you just reveal his basic lack of chem knowledge somehow (also seems like a lot of work).

I have no way to prove anything.

Then it is unclear to me why you are asking years after you could have done something,

like tipping off people who would be involved in his defense.

He has gotten away with fraud.

A lot of people do.

A friend of mine is a laughing stock within his family because it took him years longer to finish his degree than his cousin who did it in four years (plus summer school).

Except that the cousin didn't finish in 4 years, in fact he didn't even finish.

Their university allows people to "walk" in May if they can graduate using summer school.

He registered for the summer school courses, invited his family to see him walk, walked (with them watching), dropped the courses, and got his parents money back.

He doesn't have the degree like your relative does, but since everyone in his family thinks he does it is kind'a the same thing.

Let it go.

I think an important point is clearly missing in the other answers:

If the goal of a PhD is to make science going forward, he reached the goal ! Perhaps in a non standard way and, in my opinion, by far not the easiest way. Nevertheless research went (a bit) forward thanks to his ability of making other people work for him.

So, not only you should let it go, but I think you should also respect the fact that he could "cheat" a whole study plus PhD which sounds like an almost impossible task for me.

Maybe you should suggest him to do a degree in management. Sounds like it would really fit him.