Former Chairman Ahn Cheol-soo of the minor opposition People's Party has called on President Park Geun-hye to resign.
Ahn delivered the demand in a news conference on Wednesday, saying that Park has already been let go of her qualification as president politically and ethically.
He said a new leader should be selected no later than the first half of next year.
While likening Saturday's massive antigovernment rally to a civil revolution, Ahn added that South Korea is not the president's personal property and she must step down if she cares about the nation.
He said that public outrage will grow stronger if the prosecution fails to completely dispel suspicions with the president left untouchable.
Source: KBS World Radio