SACRAMENTO, Calif. (AP) — An Arizona nonprofit disclosed Monday that two conservative groups were behind its $11 million campaign contribution to a California organization fighting Gov. Jerry Brown’s tax initiative, but the revelation shed little light on who provided the money since those groups don’t have to report their contributors.

The California Fair Political Practices Commission, the state’s political watchdog agency, termed the donation from Americans for Responsible Leadership the largest case of “campaign money laundering” in state history.