my question is about what happens to x. not about me or others. what law does to the person who possesses the stolen property provided all proof, agreement in place that the owner is not paid
You're still assuming that the software is "stolen." But it isn't "stolen" if the seller had the right to sell it to X -- and the seller could very well have that right even if he did not financially compensate you for your contribution to the creation of that software.
As Bruce notes, if some of the code qualifies as a trade secret and X was provided that code [along with the software itself] then the analysis of whether the sale to X was lawful or not gets complicated because the seller may NOT have had the right to convey to X those trade secrets. Again, your own attorney needs to dig deep into the facts. For your part, do NOT assume that X is in possession of "stolen" software -- and certainly do NOT publicly accuse him of that or else YOU will be on the wrong end of at least a defamation lawsuit.
its not a license, they sold the entire product and got money and cheated me by not paying anything for my work.
Yes, perhaps the other co-authors of the software "cheated" you out of your share of the proceeds of their sale to X. So, for the last time, hire an attorney to look into the matter.