Police said Friday that they are considering manslaughter charges in the Grenfell Tower fire in London, adding that the blaze started in a refrigerator freezer, the BBC reported.

The police investigation is focusing on how the fire began, how it spread and who should be held responsible, Detective Chief Superintendent Fiona McCormack told a press briefing. Documents already have been seized, CNN reported.

Insulation on the building also failed tests, the BBC reported.  CNN reported that investigators are focusing on the role that cladding, apparently used in recent renovations of the tower, may have played in the blaze.  McCormack said the cladding samples sent for analysis failed safety tests.

Seventy-nine people are missing or presumed dead after the fire on June 14 destroyed 150 homes, the BBC reported. Police confirmed the fire had not been started deliberately.

McCormack said the department’s priority was “to understand who was in Grenfell Tower,” and wanted to hear from anyone who was in the building on the night of the fire.

“I do not want there to be any victims of this tragedy that we do not know about,” she told the BBC.