What to do when I suspect Research Integrity Office of covering up malpractice
Your first mistake was to report the irregularities to the relevant university. If that was the university of the offender, then their primary interest is to deflect/reduce any possible damage to their institution. Clearly, publicly uncovering unethical behaviour within its own university does not serve this purpose.

There have been documented cases in the UK, where the public reporting by the head of department (HoD) of plagiarism resulted in the sacking, not of the offender, but of the HoD, because of damage done to the University.

If you're seriously concerned, you should expose this to the editors of the respective journals or, better, to the public. The problem with the latter is, of course, that you may make strong enemies. One option may be to find allies, i.e. influential senior researchers in your field who are prepared to co-author any publication and/or to support/sign your letters to relevant editors.

In the end of the day, malpractice like this is drowned in the scientific discussion. If the results cannot be reproduced in independent studies, then they loose credibility and will be ignored. So perhaps, you should not spend too much frustrating effort on this.