Hey guys and gals! Here is my 100% Achievement Guide for Infliction!
So after you complete the game and the credits finish rolling, you will have to walk through what looks like a grotty piece of hell hallway until you reach an open door on your right. (There is only one path)
Once through this door, you have 4 doors to choose from.
NOW, i had to replay this twice as i first went through the very very right hand side door and it didn't unlock.
My second time through i went through the (3rd you could say) door which is directly ahead of you but slightly to the right (The one with the Ring style ending of the ghost coming out of the tv) and it unlocked.
So my advice would be to go for the the same door i went through. But it's no guarantees it will unlock first time, so just let me know in the comments if it worked for you or didn't
Go to 57:00 in my video to see where and how this unlocks.
Hope This Helps!