the suspects must at least be readers of the thread since they are trying to hide who they are. just give up hiding and leave, kano will find you.
i say out the thieves and give them the ban hammer.
Cant ban them, they use a proxy and mining with a btc address both can be changed, it sucks and I don't know why the would hang out and waist electricity.
Their IP(s) could be banned, however Kano has done the best thing and is withholding payment (pending blocks) which means little/no downside for the pool. They either start finding blocks and get paid, or now waste their time and electric by worthless mining. Either of which is ok with me, although I would prefer them to find blocks.
As for why they do it is because, they (did) get rewarded for providing work (that is like all of us mining here), however withholding found blocks doesn't hurt them as they got paid for their work regardless (albeit with less block rewards) and only served to hurt the pool overall.
Again kano has done the sensible and best approach for the pool, with a bit of extra work for him regarding payments. If they change their ways and bring in the blocks then great, if not then kano can let them waste their hash or perm ban them.
I would love to know the hash power amount they have.
Here is why.