Well, it's clear that the Knights weren't supposed to be official, for all the hints that, yes, maybe the government was behind it. And the Psi Corps don't really have that kind of plausible deniability - all the teeps are Corps, and it's not like it's easy for rogues to get around. Plus it would pretty much have to be Psi *Cops*, and - even harder to convince people that they weren't official.