"Perhaps there was a short circuit. The investigators raise questions about the lifting mechanisms used in the repair work," a source said.
Earlier, a construction company, Europe Echafaudage, which was engaged in the restoration of the cathedral, stated that it complied with all safety requirements and protocols.
READ MORE: Pope Francis Thanks Notre Dame Firefighters on Behalf of Catholic Church
The devastating fire broke out at the Notre Dame de Paris on Monday evening, resulting in the collapse of the cathedral's spire and two-thirds of its roof.
After the tragic fire, French authorities, businessmen, public organisations and societies campaigning for the protection of historical monuments immediately began to raise funds for the restoration of the iconic cathedral.