The latest Wall Street watchdog to leave for the private sector is Richard Zabel, the trusted prosecutor who helped Manhattan US Attorney Preet Bharara conduct a wide-ranging investigation into insider trading.

A memo reviewed by The Wall Street Journal said Zabel is leaving to join Elliott Management, a hedge fund firm that has waged high-profile campaigns against the government of Argentina and companies in Silicon Valley. He will serve as the firm's general counsel and join in September, according to the memo.