The abiding question among all the many mysteries interwoven in the dramas of Haymarket remains "Who threw the bomb?" Some people, including Albert Parsons, charged that it was the work of an agent of capital out to discredit labor organizers like himself. But most people at the time and since, regardless of which side they were on, believed that the likely bomb-thrower was anarchist Rudolph Schnaubelt.

Schnaubelt, pictured here in the handwritten "wanted" poster issued after the bombing, was indicted along with the others, but he vanished from Chicago and so escaped prosecution (see "The One that Got Away" entry in the "To the Bar of Justice" section of Act III).

Another lingering question is who made the bomb used in the Haymarket, with opinion divided over whether it was, as the state argued, defendant Louis Lingg. Lingg certainly did make bombs of a kind very similar to that used on the evening of May 4, but it is hard to prove that one of his bombs either was or was not used in the Haymarket.

Near the end of his masterful book The Haymarket Tragedy, published in 1984, historian Paul Avrich includes a chapter in which he tried to solve this mystery. Sorting through the evidence and the contradictory theories, Avrich suggests that a likelier suspect than Schnaubelt was a militant anarchist shoemaker named George Schwab. (George Schwab was no relation to Haymarket defendant Michael Schwab, whose sister was married to Schnaubelt.) Schwab was supposedly in Chicago briefly in the course of moving from New York to California. Avrich remarks, however, that the evidence pointing to George Schwab was "far from satisfactory."

A year later another candidate surfaced. Dr. Adah Maurer wrote to Avrich suggesting that her grandfather, George Meng, who lived on a farm just south of the city, was the bomb-thrower. Meng, a dedicated anarchist, had attended the Pittsburgh Congress in 1883 along with Albert Parsons and August Spies (see "The Pittsburgh Manifesto" entry in the "From the Archive" section of Act I). According to Dr. Maurer, her mother (i.e., Meng's daughter) not only told her that Meng was the bomb-thrower, but also recalled a man named Rudolph hiding briefly at the Meng farm. This squares with the most reliable account of Schnaubelt's escape in stages from Chicago and the United States.

Commenting on Dr. Maurer's account in The Haymarket Scrapbook, the extensive compendium of materials collected edited by Dave Roediger and Franklin Rosemont for the Haymarket centennial, Avrich writes, "Dr. Maurer's story has the ring of truth, and I am inclined to believe it."