A fire that killed six men at an apartment building in Fukuoka Prefecture about a year ago could have been a case of arson, investigative sources said Tuesday.

Police have found security camera footage showing a suspicious person walking around the two-story wooden apartment in Kitakyushu around the time the fire broke out, late in the evening of May 7, 2017.

There is also a witness account of a person walking toward the apartment and returning the same way a few minutes later, the sources said.

The police suspect the person entered the building and started the fire in the northern hallway on the first floor. The apartment building and a neighboring residence burned down.

Based on testimony from residents, police believe the fire was unlikely to have been an accident, they said.

The two-story apartment building, which was over 60 years old, consisted of 16 residential units, a dining room and a bath.

Many of the residents were day laborers and all were living alone. The occupants, many of whom stayed for short periods, paid rent every 10 days, according to a survivor.