After you finish the story on Killer, you'll have the opportunity to go through again (on Killer, of course) and beat it in under one hour and twelve minutes. You could try to do it legit, in which case I wish you the best of luck. Cover and bullet curves are your best friends. However
, if you wish to do it nice and quick-like, HE4VENSENT
figured out a little shortcut. Start up the Time Attack mode and get to a checkpoint (i.e. Right after the cutscene where you discover the cops in your place in Act 1, when it saves). Quit out, then go to "Unlocked Acts" and select Act 9 on Killer. Go through the level and you should get it upon completion. This also works for "Dr. Lobotomy" and "Butcher would be proud". If you haven't gotten Between Old Friends
before doing this one, you can select Cross as your character and get that achievement as well. If you do the Close Combat Mode and Headshot mode glitches, and then try and do the other achievements like kill the Immortal as cross, they may not unlock; this is because you need to re-glitch it back to normal. Start a new game on normal mode, then quit out.