At least three notable anomalous events occurred at the World Trade Center in the weeks and months leading up to September 11, 2001, which may have related to the imminent terrorist attacks but could not have been caused by al-Qaeda, the group supposedly responsible for 9/11.
There was an increase in security at the Trade Center in the two weeks before 9/11, for reasons that are unclear, which only ended the day before the attacks. Also, the fire alarm system in World Trade Center Building 7 was placed on “test condition” every morning in the seven days before the attacks and on the day of 9/11. While it was in this mode, any alarms would be ignored. WTC 7 was a massive skyscraper located just north of the Twin Towers, which mysteriously collapsed late in the afternoon of September 11. And some of the elevators in the Twin Towers were out of service in the months before the attacks, supposedly due to maintenance work or modernization.