ICAC investigations are normally top secret, with serious penalties for journalists or individuals who divulge confidential information.

As noted here, ongoing investigations are not publicised. I've seen people here accusing the university of being opaque and un-forthcoming with regards to this thing, but it's really not their place to be publicly disclosing information relating to the investigation. Instead, they'll publicise what they can - that he was previously put on indefinite leave, and that he recently resigned.

That Rathjen had engaged in "a personal relationship with a staff member."

From what I've read, this seems to sum it up.

The other 99% of stuff in that blog post seems to be a bunch of suppositions and accusations without much actual substance. It reads like the author has a vendetta which makes me cautious to consider it a good resource. And he uses the phrase "I have documentation but I can't reveal it" far too often for my liking. Never read this guy before so perhaps he's a solid author with good sources, but I'm dubious just from this one post.