Five people were found dead at a residence in Tokyo's Edogawa Ward in what is suspected to be a group suicide, the police said.
The bodies of a man, three women and one person of unknown sex were found at around 9 p.m. Friday in a room on the second floor of the residence, they said.
The five were found lying in a sealed room where charcoal had apparently been burned. The entrance was locked and its window was sealed with packing tape, they added.
A 37-year-old man who lived there is unaccounted for. He contacted a Twitter friend around Tuesday, mentioning his desire to die with others interested in ending their lives.
The Twitter friend informed the police about the man on Friday, leading to the discovery of the five bodies. Authorities believe the resident is among the dead.