The Justice Department's Bureau of Investigation (BOI, the forerunner of the Federal Bureau of Investigation, or FBI) did not immediately conclude that the bomb was an act of terrorism. Investigators were puzzled by the number of innocent people killed and the lack of a specific target, other than buildings that suffered relatively superficial, non-structural damage. Exploring the possibility of an accident, police contacted businesses that sold and transported explosives. By 3:30 pm, the board of governors of the NYSE had met and decided to open for business the next day. Crews cleaned up the area overnight to allow for normal business operations, but in doing so they destroyed physical evidence that might have helped police investigators solve the crime. The Sons of the American Revolution had previously scheduled a patriotic rally for the day after (September 17) to celebrate Constitution Day at exactly the same intersection. On September 17, thousands of people attended the rally in defiance of the previous day's attack.