The spies that escaped implicated the other rebels in their bid to escape pursuit. That way more than the 10,000 that infiltrated his kingdom were captured. It provided him with a lot of experimental materials. It is what they should do. After all, he saved their lives from wicked Origin gods that made them into suicide bombers.
Then again, the Origins may not be completely wicked. After all, they granted the rebels a way to resist the kingdom of life. The mark they were given wasn't useless. It hid the rebels from his sight just as it was promised to do. He couldn't see them but he could see traces of their absence.
It was like seeing the footprints of an invisible man walking on sand. He was startled when he first saw the footprints but couldn't see what created them. That's how he knew that something was up.
