On this date in 1920, an unidentified man stopped his horse-drawn cart in front of the J. P. Morgan building on Wall Street. He got down from the cart and disappeared into the noontime crowd. A short while later, a bomb consisting of dynamite and cast iron slugs detonated on the busy street. Thirty-eight people were killed and over four hundred were injured. Police conducted an exhaustive investigation that lasted over three years, but the case was never solved.
The Street.com: “Previous Terror on Wall Street — A Look at a 1920 Bombing”
Wikipedia: “Wall Street bombing”