It has been said that the catastrophic fire that ripped through the Paris landmark was “potentially linked” to a $9.5 million renovation project on the church’s spire.
But on Thursday, an unnamed judicial police officer said investigators now believe the blaze was sparked by an electrical 'short circuit'.
Investigators still don't have the go ahead to search for clues within the rubble for safety reasons.
The 850-year old building rapidly set ablaze at around 6.40pm local time on Monday evening; by 8pm, the fire had ripped through the cathedral's famous spire.
The cathedral was at the start of the restoration project.
The probe took place as President Emmanuel Macron led a day of tribute to firefighters who saved the cathedral from burning to the ground entirely.
President Macron held a ceremony at the Elysee Palace to thank the hundreds of firefighters who tackled the blaze overnight.
The roof of the cathedral and the famous spire was made from centuries-old oak wood tree covered in lead and was consumed by the raging fire.
The damage was so bad that the monument is currently being reinforced with wooden planks to support parts of the structure.
But Notre Dame's famous bell towers, rose windows, organ, and precious artworks were saved.
Meanwhile, local police have closed off a large part of the island where the cathedral is located, due to ‘important risks’ of collapse and falling objects.
The president said firefighters would be awarded medals for their bravery and hard work.
He said: ‘We've seen before our eyes the right things perfectly organised in a few moments, with responsibility, courage, solidarity and a meticulous organisation.
‘The worst has been avoided.’
Mr Macron vowed to have the world-famous place of worship restored within five years.
Officials have said a temporary wooden wooden cathedral should be built in the shadow of Notre-Dame's famed towers while the building is being repaired.
Earlier on Thursday, the fund to help rebuild Notre Dame Cathedral was said to have hit the one billion euro mark.
According to reports, TV personality Stephane Bern said on Wednesday that a billion euros has now been pledged to help rebuild the monument after it was ravaged by fire earlier this week.
Some of the donors include French billionaires Bernard Arnault, chairman of luxury goods group LVMH, and Francois Pinault, who pledged 200 million euro (£173 million) and a reported 100 million euro (£86 million) respectively.
L'Oreal Group, the Bettencourt Meyers family and the Bettencourt Schueller Foundation has also jointly also pledged 200 million euro.
French oil and gas company Total said it would give 100 million euro towards reconstructing the "architectural jewel".