Ukrainian investigators on Tuesday said they had opened a criminal case into suspected extortion by officials at a sister anti-corruption agency, based partly on information from a whistleblower who also implicated the president’s office. The National Agency on Corruption Prevention (NAZK) is a keystone of Western-backed reforms but has been criticized for making slow progress with its main task of verifying officials’ wealth declarations for evidence of ill-gotten gains. NABU - a sister agency investigating high-profile corruption cases - said it opened the case against NAZK officials on suspicion they received “undue benefits in especially large amounts, combined with the extortion of such benefits.” Officials at other state bodies are also being investigated, a NABU spokeswoman said, without giving further details. While details of the case are not yet clear, the fact that a state-run anti-corruption agency is itself being investigated for corruption suggests the author...