As a verb, credit means "to put faith in," "to trust," "to believe in": "I do not hesitate to credit you with good intentions." Accredit means "to certify," "to attribute to," "to invest with power or authority": "That statement was accredited to Winston Churchill." "When he left the Senate, he was accredited as Ambassador to Peru." When some act or deed is thought of as being put to someone's advantage, either word may be used: "The discovery of this virus was credited (or accredited) to Professor John O'Reilly."
Dictionary of problem words and expressions. Harry Shaw. 1975.