6 bombing cases that were never solved

Victims of the Wall Street bombing in 1920.

Story highlights

  • The deadliest attack in NYC before 9/11 remains a mystery
  • Despite technology advancements, even some modern bombings haven't been solved

(CNN)It was lunch time on September 16, 1920 when a bomb went off in New York City's Financial District, killing more than 30 people and injuring 300.

It was the deadliest terror attack in the city until 9/11.
    Nearly 100 years later, the case remains unsolved -- and it's not the only high-profile attack that investigators never unraveled.

    1920: Wall Street, NYC

    Scene of bombing of Wall Street on September 16, 1920.
    A horse cart exploded in front of J.P. Morgan's headquarters on Wall Street, blasting metal shrapnel and shattering blocks of windows.
    "Almost in front of the steps leading up to the Morgan bank was the mutilated body of a man," wrote reporter George Weston. "Other bodies, most of them silent in death, lay nearby. As I gazed horror stricken at the site, one of these forms, half-naked and seared with burns, started to rise. It struggled, then toppled and fell lifeless into the gutter."
    New York police, the Secret Service and the Bureau of Investigation (which preceded the FBI) tried to figure out who was responsible, but came up with few leads.
    Letters from the "American Anarchist Fighters" were found in the area before the bombing, and they seemed similar to ones from two earlier bombings connected to Italian anarchists.
    "The best evidence and analysis since that fateful day of September 16, 1920, suggests that the Bureau's initial thought was correct—that a small group of Italian Anarchists were to blame," a modern FBI summary concludes. "But the mystery remains."
    Shrapnel still scars the nearby buildings today.

    1933: The first airplane bombing, over Indiana

    United Airlines Boeing 247
    The first-known sabotage of a plane remains unsolved to this day.
    On October 10, 1933, a United Airlines Boeing 247 flying from Newark to Cleveland and then on to Chicago exploded over Chesterton, Indiana. All seven people on board were killed.
    Headlines across the country noted the "giant" plane going up in flames.
    "Consolidation of all available evidence surrounding the accident leads to the conclusion that it was caused by a high explosive, presumably located in the area of the cargo space and t