City of London records show that his early career was as a legal clerk but that in 1854 he was convicted with others at the Old Bailey for conspiracy to pervert the course of justice and served a short prison sentence.
One of his most remarked upon talents was an apparent ability to weep at will, although legal historian Sadakat Kadri notes that his frequent opponent Francis L. Wellman "suspected that he used an onion-scented handkerchief to get in the mood".
The less extrovert but more intelligent Hummel specialised in civil law and ran the firm's thriving blackmail racket, representing chorus girls and thwarted lovers, threatening married men with exposure and well-off young bachelors with suits for breach of promise of marriage.
At its peak, operating from offices just across the road from NYPD headquarters on Centre Street, Howe and Hummel received fat retainers from a significant proportion of the criminals, brothel-keepers, and abortion providers of New York.
Howe admitted that the girl had been armed with a revolver, but successfully persuaded a jury that her trigger finger had accidentally slipped not just once, but four times in the course of an argument with her married lover.