Well, on my first play through, I blame Walker for the troubles, so I made him shot himself in his day dreams. Unfortunately, that killed him in real life. I thought shooting himself made Walker finally blame himself for the sins he committed. I mean, Konrad said that Walker can blame him for all the troubles, but I thought it will lead the soldier to a bad ending. I guess I was wrong.
So, I got the second ending by making Walker shoot Konrad, and it's a bittersweet ending. After the credits, there is a secret ending which determines the fate of Walker again. I choose the Surrender ending, and Walker was spirited away by his rescuers. Unfortunately, that "good" ending is a bad ending since Walker is mentally scarred forever. I never choose other secret endings, because Walker has been through a lot of firefights, so letting him die again isn't right.
I used the WP and killed all the civilians accidently and I didn't think I had a choice at the time so I killed the soldier who killed the thief's family. I guess it's a game that you need to play through twice.