If someone produces excellent, productive research, and that research is leaking, simply ratchet up security around the research until the leaks stop. If there is a spy, they will eventually look around at all the security measures and consider the risk to their life and liberty to be too great to justify leaking information further. At that point, leaks will stop, but good research will continue, and that outcome provides much greater utility than the alternatives.

People are often too preoccupied with persecution that they view the absence of persecuting anyone of something as wrong. In the US we are preoccupied with the idea that someone, somewhere may be doing something wrong and that we should be punishing that person because they deserve it. In this case (and in most cases) persecution didn't solve the problem, but tightened security would have.