Complex sentence: The medical staff of the SGC tried to surgically remove the Goa'uld from his body and although they were able to remove the symbiote, it turned out only to be a dead husk while the Goa'uld had already taken over Kawalsky's mind.
Split into simpler sentences: The medical staff of the SGC try to surgically remove the Goa'uld from his body. Though initially successful, the symbiote turns out to be a dead husk whose intelligence has already taken over Kawalsky's mind.