The full letter by Deputy AG Rosenstein here:
https://theconservativetreehouse.com/2017/05/09/breaking-president-trump-fires-fbi-director-james-comey/#more-132407
He lays it out in spades, and his case is supported by several former AG:s, both Republicans and Democrats.
Yes! Rosenstein collected opinions from other AG’s and sealed the argument to can Comey.