The climax of terror is reached when the police state begins to devour its own children, when yesterday’s executioner becomes today’s victim.

Hannah Arendt (1906-1975) German-American philosopher, political theorist

Essay (1969-02-27), “Reflections on Violence,” ch. 4, The New York Review of Books
    (Source)

Revised and collected in On Violence, ch. 2 (1970). See Büchner (1835).