Investigators think an electrical short-circuit was the most likely cause of the Notre Dame Cathedral fire, a police official said this afternoon.
The historic building went up in flames on Monday as tearful Parisians watched in despair.
More than 400 firefighters battled the flames to save the main structure and towers.
While the world watched aghast as the medieval cathedral was ravaged during the Holy Week of Easter.
As reported earlier this week, police opened an investigation into the devastating blaze questioning a firm of “Cathedral Restorers” to establish how it started.
Craftsmen from Le Bras Freres were working on the 850-year-old iconic building before the fire took hold.
Paris public prosecutor Remy Heitz said his office was “favouring the theory of an accident”.
But he had assigned 50 people to work on what he believed would be a “long” and “complex” investigation.
It was reported that the high altar, installed in 1989, was the only piece of architecture inside the building that was damaged.
It was hit by the cathedral’s spire when it came crashing down in the flames.
Three “irreplaceable” rose windows which date to the 13th century, at first feared to have exploded, are still intact.
Le Bras Freres had won a £5million contract to repair the wooden and lead spire. Talking about the contract last year, CEO Julien Le Bras, 32, said the goal was “not to put the building at risk”.
Huge sums have been pledged to repair the beloved Paris landmark, which President Emmanuel Macron has set a target of five years to finish.
The president said France “will rebuild Notre Dame Cathedral even more beautifully” as he addressed the nation on Tuesday evening.
Meanwhile, a hero Priest who saved some of the world’s most precious artefacts in the fire insisted: “I just did what I had to do.”
Jean-Marc Fournier bravely walked into the blazing cathedral absolutely determined to save the priceless relics about to be burnt.
Chaplain of the Paris Fire Department, Father Fournier saved the famous Blessed Sacrament and the ornamental Crown of Thorns.
He said: “I find it difficult to describe myself as a hero.
“I was both the priest and the firefighter when I worked on Monday night when I entered the cathedral when the spire was burning at its top point.
“But if being a hero consists of fulfilling a mission with passion and self-denial then maybe I have been a little bit.
“But on the floor of the the cathedral I could feel no heat or smoke.
“To watch as the cathedral was devoured by the flames inspired me with a deep sadness.
“I felt it was up to me to go beyond myself to fulfil my mission and put into place what I was trained for.
“During the 20 minute period in which the firefighters were saving the cathedral, I was evacuating the holy sacrament.
“I urged Jesus to help us if he did not want to “sleep outside” and I like to believe that General Gallet (fire chief) has made the right decision to save the belfreys and the cathedral and that my prayers were heard.”
Meanwhile, shocking interior photos have revealed the scale of the devastation showing blackened walls, holes in the roof and piles of charred rubble.