Government investigators have issued a report refuting conspiracy theories that a skyscraper next to the twin towers was brought down by explosives. The report says that fires destroyed World Trade Center 7 on Sept. 11.

Scientists with the National Institute of Standards and Technology say their three-year investigation of the collapse of the 47-story building was the first known instance of fire causing the total failure of a skyscraper.

The investigators also conclude that the collapse of the nearby twin towers broke the city water main, leaving the sprinkler system in WTC 7 without water.

The collapse of building 7 has long been the subject of conspiracy theories that something else brought down the tower.