His interest in Zet seeemed to go beyond the official reason he gave Jin, but on the other hand it's very believable he wants to get rid of any evidence, that is, the players roaming free out there. They were originally meant to be kept captive and serve as depraved entertainment. At this point it would be bad if someone connected them to the corporation, especially after all the murders. However, what he intends after that or during it in the background, is another question.