The incident came to light at Chiu Sin House in Upper Wong Tai Sin Estate after a security guard found a 25-year-old man bleeding inside a lift at 7.19am.
Just seven minutes later, a 46-year-old man was found dead on a podium of the same building, with officers suspecting he had fallen from height.
According to police, the two men were neighbours, with the attacker, the older man, living one floor below the victim.
CCTV footage showed the victim entered the lift first, followed by the suspect, who pulled a knife from his bag and attacked the victim, stabbing him in the head and upper part of his body.
After the assault, the attacker returned to his flat.
When officers arrived, they found bloodstains outside the suspect’s home. Firefighters broke into the flat after no one answered the door.
Inside, they found an open window, blood-stained sneakers, and a medical appointment slip from the psychiatric department of the Hospital Authority’s East Kowloon cluster.
Assistant district commander for crime Christie Lam revealed that police had received a report in November about the two men having an argument over noise levels. Neighbours also confirmed the pair frequently clashed over the same issue.
“According to our investigations at the scene, we learned that the attacker had submitted a request to the Housing Department to exchange his unit for another,” he said.
“According to records, the Housing Department had already given initial approval but was still waiting for a new unit to become available.”
Police are continuing their investigation.