Afghan and American officials said Wednesday that a key aide to Afghan President Hamid Karzai has been on the CIA’s payroll for years, which brings to light questions about U.S. involvement in Karzai’s government. Mohammed Zia Salehi is also under investigation for corruption for his ties to New Ansari, a money-transfer firm, and he is also a former interpreter for Abdul Rashid Dostum, the ethnic Uzbek who was considered one of the most ruthless warlords. Salehi was arrested in July and saved from jail by Karzai. Salehi’s dual role also underscores the Obama administration’s stated goal of rooting out corruption, which some consider to be the greatest threat to the Afghan government and the American mission. Another prominent Afghan official who has been found on the CIA payroll is the president’s half-brother, Ahmed Wali Karzai, who has also been under investigation for corruption. The CIA declined to comment on Salehi.