After briefly working for his family's brewing company, he enlisted in the United States Army in 1918 and eventually became a second lieutenant.

That evening, the family received a phone call saying that Hamm had been kidnapped and instructions would follow later.

At 2 a.m. on June 16, a man initially believed to be gangster Verne Sankey gave a taxi driver in Saint Paul a ransom note with instructions to deliver it to William Dunn, the manager of Hamm's Brewery.

[7][1] The Federal Bureau of Investigation launched an investigation into the kidnapping and, using latent fingerprint identification, connected fingerprints on the ransom notes to members of the Barker–Karpis Gang — specifically, Alvin Karpis, "Doc" Barker, and Charles Fitzgerald.

This was the first time that silver nitrate was successfully used in forensic science to identify fingerprints from objects that could not be dusted for prints.

[8] Hamm also served on the board of directors of First National Bank of Saint Paul and the United States Brewers' Association.