Members of the Lettish section of the Anarchist Black Cross (ABC) were constructing a bomb in a seven-story tenement when the group's large supply of dynamite exploded prematurely.

[1] In July 1914, two members of the Lettish section of the Anarchist Red Cross (ARC), Charles Berg and Carl Hanson, began collecting dynamite they had obtained from Russia.

Several meetings were held at the Ferrer Center, where the group devised a plan in which Caron, Berg, and Hanson were to plant a bomb at John D. Rockefeller's home in Tarrytown, New York.

Plunkett, a party to the conspiracy, later stated that Berkman chose to remain behind the scenes rather than take an active role in the bombing due to his being on probation for the attempted murder of Henry Clay Frick.

Fifteen minutes later, a deadly explosion took place on the sixth story of the Lexington Avenue building, located between 102nd and 103rd Streets in the thickly populated area of Harlem, only a few blocks away from the Ferrer Center.

The bomb was discovered by a gardener who found four sticks of dynamite, weighing one pound (0.45 kg) each, half hidden in a rut in a driveway fifty feet (15 m) from the front entrance of the residence.

The dynamite sticks were bound together by a length of wire, fitted with percussion caps, and wrapped with a piece of paper matching the color of the driveway, a path used by Archbold in going to or from his home by automobile.