I think he was offered staff councilling and also increased campus security due to his claims on being attacked by a person carrying a knife etc. Yes, the committee should've checked credentials much more and done more due diligence at the hiring stage.What went wrong during this process will be reviewed no doubt. Hiring a prof at any uni is not done lightheartedly. It's a huge investment and a long process.
The thing is though, how could Cambridge have known about the pathological lying issue with increasingly unbelievable stories. Many of those stories came out later. In all likelihood the story the committee heard was autism, disadvantaged background, marathon runner, which sounded like a great success story they could use and get behind.
The hiring committee wouldn't have looked at the detailed stories J came up with surrounding all this, it's not what hiring committees do. They would've discussed research, teaching philosophy and needs in that interview. They also don't plagiarism checks for every single paper and monograph of every CV. Experts read the papers and evaluate future potential and impact, but they wouldn't check for plagiarism unless a committee member has suspicions already. Once a paper is published after peer review at a reputable journal, the paper record is trusted. So in that respect we can say even the journals in question are guilty here.
Then once employed J started pushing forward increasingly incredible stories. Viva two weeks after Brain tumour operation, six day marathons, mutism, locked in syndrome... At this point other Cambridge academics would become suspicious, start to feel embarrassed by the circus but HR rules mean a lengthy inquiry process. They initially supported and defended him from the racist attacks, but at some point, after falsified visits etc they had enough evidence, or suspicion, to open up an investigation. Which they did. Soon after here we are.