Brussels Bombing Brothers Secretly Filmed Country's Top Nuclear Official, Source Says

PHOTO: Ibrahim El Bakraoui is pictured in a July 2015 image taken by Gaziantep police. Right, This photo accompanied an INTERPOL Red Notice for Khalid El-Bakraoui.PlayHaberturk newspaper via AP | INTERPOL
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The two brothers allegedly involved in the subway and airport bombings in Brussels Tuesday had previously filmed one of Belgium's top nuclear scientists, a security source told ABC News.

Khalid and Ibrahim El-Bakraoui used a hidden camera planted outside the man’s home to record the footage, according to the source, who is a security expert based in Belgium.

The video was seized during a raid in Belgium after the Paris attacks, the expert said.

The footage was at least 10 hours long and was found at the house of Mohamed Bakkali, a suspect in the Paris attacks who was detained on Nov. 26. 2015.

"We confirm the existence of this footage mentioned in the press that is linked to an individual in the nuclear industry," Belgium's federal prosecutor said in a statement to ABC News. "No information on his identity will be revealed for security reasons and no information will be given on the circumstances of the discovery of this footage which was during a raid conducted in the context the Paris investigation."

Both brothers were suicide bombers in the coordinated attacks in Brussels Tuesday morning, officials say. Khalid El-Bakraoui, 27, was one of the two suspects involved in the subway bombing and his older brother Ibrahim, 29, was one of the three suspects spotted at the airport, according to officials.