When I clicked "reply", I intended to say that it meant "he immediately confessed". But, now, I don't think that's what it means. I think that repente is locked between ita and interrogatus for a reason, yielding "Having thus been unexpectedly asked". So:
"Having been so unexpectedly asked, Medus immediately confessed to have stolen the money from the purse".
mihi iussa capessere fas est