By that very fact; by the fact itself. (OED)
"Their offences at first were those of laziness, carelessness, and impulse, rather than of malignity or ungoverned viciousness. Such misdemeanors needed discriminating treatment, firm but reformatory, with no hint of injustice, and full proof of guilt. For such dealing with criminals, white or black, the South had no machinery, no adequate jails or reformatories; its police system was arranged to deal with blacks alone, and tacitly assumed that every white man was ipso facto a member of that police. Thus grew up a double system of justice, which erred on the white side by undue leniency and the practical immunity of red-handed criminals, and erred on the black side by undue severity, injustice, and lack of discrimination."
- W.E.B. DuBois, The Souls of Black Folk, 1903