Well, there you go making assumptions. Step 1: find out if the prisoners have, in fact, been moved out of Mandate space. If not, then you should keep all your options open, including petitioning the Mandate for redress if those warclones weren’t an actual threat to anyone. I’m not saying they’ll help, but before you assume they won’t, you might want to hire some legal specialists to figure out if there’s a way they can be persuaded.
It’s not about conflict with the Ammatar, it’s about learning to work within the various legal systems to avoid conflict. The more you work within the framework the various sovereign entities have established for resolving disputes, rather than ‘let’s blow something up’ or ‘let’s go making public accusations’, the less likely you are to, I dunno, get declared foreign slavers, and so forth.