Investiators now say a gas leak in a heating system caused the fire that killed five teenage girls at an escape room in Poland.
Firefighters previously blamed poor electrical wiring and lax security procedures for Friday's blaze, which also caused a 26-year-old man to suffer burns.
The school friends were celebrating one of their birthdays at the escape room in Koszalin, in northern Poland, and are believed to have killed by carbon monoxide inhalation.
Koszalin prosecutor Ryszard Gasiorowski said a leak in the bottled gas heating system was a probable cause of the fire, which broke out around 5pm local time.
"The immediate cause of the fire was from the unsealing of gas cylinders which were installed in the heaters inside this building," he said.
"There were four devices (heaters). They were in the waiting room of the games' room. That's where the fire started. The fire had cut off the employee who was supposed to supervise the participants of the game and help to unlock the door."
What are escape rooms?
The escape room game, which is popular in the UK, sees players seemingly locked inside a room or building.
The players must find clues that help them get out.
The UK centres are monitored by staff throughout and players are made aware they can take an exit door in the case of emergency.
What are Polish officials doing about safety after the fire?
Poland’s firefighting chief, Leszek Suski, said that electrical wiring at the location was makeshift and too close to flammable materials, while the man in charge was probably not there when the fire broke out.
Investigators launched an inquiry into the cause of the fire as Interior Minister Joachim Brudzinski Brudzinski ordered fire safety controls in all escape rooms.
Prime Minister Mateusz Morawiecki has sent condolences to the victims’ families.
President Andrzej Duda said on Twitter it was a "crushing tragedy" that five young girls died so early in their lives.
Koszalin Mayor Piotr Jedlinski announced that Sunday would a day of mourning in the city.