To what extent do actions change intentions?

In the "Utterly Perfect Murder" by Ray Bradbury the main character is named Doug and he is having his 48th birthday when he decides that he wants to kill one his close friends but also one of his main enemies from 36 years ago. In the middle of his sleep he wakes up and exclaims that he is going to go kill Ralph Underhill. When he gets to his house he decides not to use gun but instead to kill him only in his imagination. In the story it says, "At some secret bloody level I had always known I would not use the weapon. I had brought it with me yes, but time had gotten here before me, and age, and smaller, more terrible deaths.... Bang." This shows that his intentions might have been to kill Ralph Underhill but instead he only killed him in his imagination, he might have thought it might be better not to go to jail but rather to just kill with 6 imaginary bullets to the heart.