The investigation is coming to a close just as the cathedral prepares to reopen early next month.
Notre Dame's bells rang on Friday for the first time since the fire, ahead of its reopening ceremony on Saturday, December 7.
But investigators have yet to identify who, if anyone, was responsible for the fire, pictures of which have travelled around the world.
"Since the beginning of the investigation, all possibilities have been explored, including the hypothesis of a human role in the occurrence of this fire," said Paris Attorney General Laura Becqueau in April.
"But the truth is that the closer we get to where the fire occurred, and the more analysis results we get, the more difficult it is to establish the cause of the incident," she added.
In 2023, investigating magistrates have requested new examinations of the debris from the cathedral, the site where the fire started and the church's "technical infrastructure".
Although these had all been carried out by April, the experts were asked to summarise and collate their technical conclusions to see if it was possible to determine a potential cause of the fire.
Prosecutors told AFP this week that investigators have now ordered "a 3D simulation of the fire's onset to be created using photos taken at the time.
So far, no charges have been filed against anyone, prosecutors confirmed.
A source familiar with the case said the investigation was nearing completion.
Remy Heitz, Paris's chief prosecutor at the time of the initial investigation, said at the time that he believed it was most likely an electrical fault or a forgotten cigarette.
Since then, no new information has emerged to suggest deliberate arson.
"Over the past year, every area (in the cathedral) has been cleared of debris" - with no new relevant evidence uncovered, a judicial source said in mid-2023.
The more than 850-year-old Notre Dame Cathedral, famous worldwide, was undergoing restoration when the fire broke out on April 15, 2019.
Several safety lapses were later pointed out, including the cathedral's alarm system, which contributed to delays in firefighters' response, and the electrical system in one of the elevators.
None of those factors are believed to have caused the fire, but they did allow the flames to spread. | BGNES, AFP
