In what ways is the narrator careful about the means he uses, and careless about whether his act is justified in "The Tell-Tale Heat"?

The madness of the narrator in "The Tell-Tale Heart"
prohibits him from thinking rationally, and it is obvious that there is no justification
in killing a man because he has an evil eye--a "vulture eye." Further, he admits that he
loves the man and that he has no intention of stealing his money. The narrator is
careful about taking precautions to keep the old man from uncovering his plot to kill
him, however. He "was never kinder" to the old man in the days before he planned to kill
him, and he slowly and "oh so gently!" opened the door each night, taking an hour to
place his head inside the room. But for seven nights, he could not kill the old man: The
eye was always open. On the eighth night, he took similar precautions, but his chuckling
may have alerted the old man; his slip of the latch awakened him. These noises caused
the man to open the eye, and it gave the narrator the excuse to finally fulfill his
goal.