To unlock each ending, you must finish the game a certain way. For ending P, you'll need to:
Optional: You can start at Bracciano (level 2 below)
Level 1 - Keep right.
Intermission 1 - Nothing.
Level 2 - Win or lose the race, keeping right.
Intermission 2 - Leave Olga ("better to be apart").
Level 3 - You have to question the priest's beliefs and you will do it with these three topics:
So tell me about your job, Padre.
So what? It's still a job, isn't it?
"Vocation." So, you hear voices?
But you don't…? Has he stopped talking to you?
I'm sorry, Padre.
What do you think about the Moro kidnapping?
Yeah, the so called "firm line."
If only we could help somehow…
I'm curious… What do you think of Paul VI?
He said some strong words on Aldo Moro's behalf.
Where do you think Italy is headed, Padre?
Finale - There will be a conversation and you'll need to say the following:
Why is religion always about giving things up?
Faith in what, Padre? Faith in whom?
And women. And children. And everyone in need.
Video courtesy of Dernop