Daniel is stupid. (spoilers)

[Empow3rd]

My opinion is that he drank the potion so that he would have no regrets killing Alexander. He wanted Alexander dead but he knew all the horrible things he had done so he just couldn't do it. That is why in the first note you receive, Daniel just tells "you" to kill Alexander and that is pretty much all the details he gives to you.

[Spooder Wekd]

Someone was not reading the notes very much. He was basically psychosomatically paralyzed by what he had done, he needed to forget to have the strength to kill our buddy al. Thats why he left himself notes to guide himself.