Curious that he claims that he made no personal gain. Why then was he submitting false invoices?
It is , of course, immaterial whether he got any direct financial benefit; a man who deliberately falsifies, or makes false, records for such an accounting purpose is guilty whether or not he makes money from the falsity. That is a necessary legal provision precisely because someone who submits false accounts may, by so doing, make it impossible to prove what losses or gains are hidden. And someone may submit false or falsified documents in the hope of getting promotion or to keep their job, by hiding their own incompetence, or for any number of other reasons which don't bring them immediate financial reward or produce any recognisable financial loss to another.
So, in short, he should be prosecuted, on the material now disclosed (or previously disclosed, on the face of it)