Two people were found dead Monday following an explosion at a corporate dormitory in Itabashi Ward, Tokyo, police said.
Police opened a murder investigation after the skulls of Masanori Nagamoto, 44, and his wife, Keiko, 42, were found to have been caved in.
The bodies also both had stab wounds in the abdominal region. Kerosene had been spread in the room, and the gas hose was found severed, police said.
Investigators are looking into the cause of both deaths and the explosion.
The two were found in the kitchen of the caretaker's room, police said. Both were working as janitors at the dormitory.
The three-story building is owned by Sato Kogyo Co. and another company, and is located in a residential area near Narimasu Station on Tobu Railway's Tojo Line.
No other residents in the dormitory were injured.
The explosion occurred in the caretakers' room on the first floor at around 4:40 p.m., police said.