You’re underselling it. If he was the guard from this article:
Davis knocked him out by “throwing a beer stein” at him. The Thirties was a hell of a decade.
My dad contacted an FBI historian to get his uncle’s full story. Hoover, nemesis of corrupt big city machine police, wasn’t predisposed to hiring Irish Catholics in the first place. Making them agents who then bought their captives beer was beyond the pale.