Five years of investigation and expert reports have failed to identify the precise cause of the 2019 fire that ravaged Paris' landmark Notre Dame cathedral, even as the probe draws to a close just as the cathedral prepares to reopen early next month.
Notre Dame's bells rang out Friday for the first time since the fire, ahead of a reopening ceremony on Saturday December 7.
But investigators have yet to establish who, if anyone, is responsible for the fire whose images went around the world.
"Every avenue, including the hypothesis of a human role in the origin of this fire (has been) explored since the beginning of the investigation," Paris' chief prosecutor Laure Beccuau said in April.
"But the truth is that the closer we have got to the spot the fire started, and the more results of analyses come back, the more weight is lent to the theory of an accident," she added.
Beccuau noted at the time that investigating magistrates had in 2023 called for new expert reports on the cathedral debris, the place where the fire started and the church's "technical infrastructure".
Although all had been carried out by April, the experts have been asked to summarise and cross-reference their "extremely technical" findings "to see if it is possible to determine a potential cause for the fire", she added.
Prosecutors told AFP this week that investigating magistrates have now ordered "a 3D simulation be created of the start of the fire using the images taken at the time. This simulation will allow us to compare different theories" about the blaze.
So far "no charges have been filed" against anyone, the prosecutors confirmed.
A source familiar with the case said the investigation was drawing to a close.
Remy Heitz, chief Paris prosecutor at the time of the initial investigation, said at the time he believed an accidental cause such as an electrical fault or smouldering cigarette butt was most likely.
Since then, no new information has surfaced to suggest a deliberate arson.
"Over the past year, every zone (in the cathedral) has been cleared of debris" -- without revealing any new relevant evidence, a source in the judiciary said in mid-2023.
The more than 850-year-old cathedral of Notre Dame, whose silhouette is known the world over, was undergoing restoration work when fire broke out on April 15, 2019.
In a spectacularly destructive blaze relayed around the world in images and live broadcasts, the church lost its spire, roof, clock and part of its stone vault.
Several safety failings were later singled out, including the cathedral's alarm system which contributed to slowing firefighters' response, as well the electrical system in one of its elevators.
Neither is believed to have initially set off the fire, but they enabled the flames to spread through the monument.
Investigators have a separate case open into the potentially harmful health effects of the Notre Dame fire, which has also filed no charges so far, prosecutors said.
A health association joined forces with a union and two parents of local schoolchildren for a 2022 criminal complaint that accused authorities of failing to take every precaution to prevent lead pollution.
Supported by its "forest" of wooden beams, Notre Dame's roof and spire were covered by around 400 tonnes of lead, a toxic heavy metal that went up in smoke with the fire -- some of which likely came back down to earth in the neighbourhood.
The weight is "four times the total annual lead emissions into the atmosphere for all of France," the plaintiffs pointed out.
Possible charges for the lead's impact on the health of both local residents and workers sent in to decontaminate the Notre Dame site are being investigated by the same judge, a judicial source said.
