Notre Dame de Paris Cathedral,
Notre Dame de Paris Cathedral,iStock

A Paris police official said on Thursday that police investigators believe that the devastating fire that ravaged the Notre Dame Cathedral on Monday was caused by an electrical short-circuit.

However, although investigators carried out an assessment of the cathedral on Wednesday, a judicial police official told the Associated Press that the investigation is not complete since permission has not yet been granted to investigate the burned interior of Notre Dame due to safety concerns. The official said that the walls of the cathedral are currently being supported by wooden planks.

The 850-year old historical landmark in the French capital was engulfed in flames on Monday. The fire rapidly spread to the cathedral's 150-year spire, leading to its quick collapse. The cathedral, which had developed deep cracks in recent years, had been undergoing extensive renovations.

Investigators, who are currently operating under the assumption that the fire was accidental, questioned renovation workers as well as cathedral staff, interviewing dozens of people by Thursday. About 50 investigators are carrying out the probe, according to the Guardian.

Non-accidental causes have not been entirely ruled out yet by investigators but don't appear likely. "While the prosecutor's office does not rule out any hypothesis, we remind that at this stage, nothing in the investigations highlights a criminal origin," a statement by the prosecutor's office said. "Accidental causes remain our privileged lead."

The cathedral's spire and roof were ravaged in the fire but much of the interior was spared and dozens of priceless pieces of arts and artifacts were rescued as well as its organ. Its bell towers were also spared.

According to Bertrand de Feydeau, vice president of the preservation group Fondation du Patrimoine, the roof cannot be rebuilt to its original design. De Feydeau told AP that the roof's wooden beams cannot be restored because "we don't, at the moment, have trees on our territory of the size that were cut in the 13th century."

It will take years for the cathedral to open again. President of France Emmanuel Macron said he wants it to be rebuilt in five years in time for the 2024 Summer Olympics, which will be held in Paris. However, some restoration specialists estimate that it could take 15 years.

More than $904 million in donations have been gifted to Paris for the restoration of the cathedral.