The wagons cargo: 100 pounds of dynamite laden with 500 pounds of cast-iron sash window weights.
At 12:01 p.m., the bomb detonated, and the sash weights became deadly missiles that cut through the crowded lunchtime street. Shattered glass rained down from the surrounding buildings.
Thirty people died instantly, along with the wagons horse. Eight more later died of injuries; 143 people were seriously injured, with hundreds more sustaining minor injuries. It was the deadliest terror attack in American history at the time.
The initial police investigation considered the possibility that the explosion was an accident. Impeding the investigation was the decision by the New York Stock Exchanges board of governors to open as usual the next day. The bombing site was cleaned up within hours, possibly depriving the investigators of valuable evidence.
The presence of the sash weights, designed to act as deadly shrapnel, confirmed to investigators that it was an intentional act of terrorism. Because of the target, officials believed the perpetrators to be anti-capitalist radicals of some stripe.
Investigators looked into anarchists, communists, Soviets, Bolsheviks and others, but found no solid evidence. The prevailing theory today is that the attack was committed by Italian anarchists, possibly as a response to the arrest several months earlier of Sacco and Vanzetti, but no suspect has yet been conclusively proven as the culprit.
The only memorials to the attack are the shrapnel craters which still pockmark the facade of 23 Wall Street.