Some details of the chronology of Monday's fire are beginning to emerge.
At 6:20 p.m. local time (12:20 p.m. ET), security guards at the Notre Dame first heard the fire alarm and evacuated the cathedral, even though they didn't see any sign of a fire, a spokesman for the Paris fire brigade told CNN.
The fire alarm rang again at 6:43 p.m. local time (12:43 p.m. ET). That's when the cathedral’s security officers noticed the fire, Paris Prosecutor Rémy Heitz confirmed during a press conference on Tuesday.