New Delhi, Aug. 7 -- The wife of South Korea's ousted former President Yoon Suk Yeol appeared for questioning by a special prosecutor Wednesday, as investigators expanded a probe into suspicions of stock manipulation, bribery, and interference in party nominations.

The investigation into Kim Keon Hee is one of three separate special prosecutor probes launched under Seoul's new liberal government targeting the presidency of Yoon, who was removed from office in April and rearrested last month over his brief imposition of martial law in December.

The conservative's abrupt and poorly planned power grab on Dec. 3 came during a seemingly routine standoff with the liberals, whom he described as "anti-state" forces abusing their legislative maj...