The neighbor is being nice to the old man while the old man is unable to do things for himself. But the neighbor disliked the old man's vulture eye
The neighbor Can't stand the sight of the old man's vulture eye, so he planned to kill the old man.
The neighbor watched the old man every night. He spent hours just putting his head through the door. He would always shine a very small ray of light on the old man's vulture eye, but it would always be closed.
The man kills the neighbor with the old man's own mattress. Afterwards he dismembered
The man put the old man under the floor boards, and luckily there was no trace of blood anywhere in the house. Not long after the police came and said someone reported hearing some screaming
The police stayed and started drinking and laughing, but the neighbor's guilt got the best of him and he thought the police were laughing at him. So he showed them the the hidden body and they took him to jail.