The fire brigade on Wednesday afternoon confirmed earlier media speculation and initial indications and pointed to a propane gas leak as the reason behind a strong explosion and scorching fire at a cookie and biscuit plant near the central Greece city of Trikala in the early morning hours of Monday.

Five female workers on the “graveyard shift” were killed in the explosion at the Violanta plant.

In an announcement, the fire brigade said the leak was estimated to have continued over months and from pipes in the ground, ultimately building up to extremely high concentrations. Some type of sparked is estimated to have ignited the gas.

“This significant propane leak, through the ground, moved about 25 meters and was trapped in an underground space, where, in the presence of sparks caused by the facility’s electrical and mechanical equipment, led to an explosion,” a fire brigade spokesperson said.

In a related development, three individuals arrested for the deadly workplace accident – the owner, the head of production and the shift supervisor – were led before an investigating magistrate in Trikala on Wednesday afternoon.

The trio face a charge of involuntary homicide, among others.