It pays off to know your hostage! An opponent, when taken alive always yields 10 Infamy if we already know who they are. Otherwise, our ignorance, coupled with vigor, can, uhm, backfire badly if we capture too many 'innocent bystanders', pesky govt personnel, mutant rebels who ended up in a bad place at a bad time etc. In such a case, we might consider cutting our losses by disposing of any witnesses... (In contrast, catching high ranking enemies generates more Infamy if they're unknown to us yet - it increases Gals' morale!)