Recording CNA Paris as emergency crews pick through the charred remains of Notre Dame cathedral’s ancient wooden beams, which turned the world-famous site into an inferno on Monday night, focus has turned to the investigation into how the blaze started.

Thirty employees working at the Paris landmark before the fire broke out were interviewed by Paris prosecutors on Tuesday, the Paris prosecutor’s office said. They included construction workers and Notre Dame security staff.

Interviews will resume on Wednesday, the prosecutor’s office said, adding: “Investigations continue to search for the truth and identify the origins and causes of the fire.”

On Tuesday, prosecutor Remy Heitz told CNN the cause of the fire was “likely accidental,” and that “nothing shows that it’s an intentional act.”