Yonhap News Agency reported the 38-year-old aide, surnamed Hahm, had been in charge of accounting for Park's campaign during the 2008 election to choose the chairman of the Grand National Party.
Yonhap said prosecutors were widening their investigation into the alleged bribery and plan to soon summon two other aides involved in Park's campaign to become chairman -- top policy secretary Cho Jeong-man and top state affairs secretary Lee Bong-gun.
Prosecutors are investigating GNP lawmaker Koh Seung-duk's allegation Park, 74, gave monetary gifts to GNP lawmakers to win support for his bid during the 2008 party convention.
Koh had said this month he received an envelope containing $2,269 before the election.
Park, who Yonhap said is considered close to President Lee Myung-bak, served as party chief two years and became parliamentary speaker in 2010.