Even after more than 75 years, the May 6, 1937 explosion of the Hindenburg zeppelin remains one of history's most notorious aircraft disasters. Although the footage of the burning dirigible has been endlessly studied, the conclusive cause of the explosion has remained a mystery. Some people thought it was struck by lightning. Others blamed sabotage, or flammable paint. A more recent theory supposed that engine sparks ignited the hydrogen filling the airship.

Now a team of experts say they know what caused the explosion: static electricity. Long theorized as a possible cause, static electricity likely built up after the Hindenburg passed through lightning storm, which then ignited the excess hydrogen that built up in the back of the dirigible. Though static electricity was long theorized as a possible cause, one final peice of the puzzle only recently fell into the place: The men who grabbed the landing robes to moor the vehicle added the final ingredient by "grounding" the Hindenburg, creating a spark caused by connecting two opposite charges.

British aeronautical engineer Jem Stansfield and a team from the South West Research Institute in San Antonio, Texas, testing all of the theories about the Hindenburg's explosion by building 78-foot scale models of the ship. They also studied archival footage and eyewitness accounts.

"I think the most likely mechanism for providing the spark is electrostatic," Stansfield told The Independent. "That starts at the top, then the flames from our experiments would've probably tracked down to the center. With an explosive mixture of gas, that gave the whoomph when it got to the bottom."

A new documentary about the disaster and Stansfield's experiments will air this week in the U.K.

You can view footage of the Hindenburg disaster below: