TAIPEI — Taiwanese investigators were expected to rule Sunday on the further detention of a former candidate amid graft allegations that have sparked minor street protests by his supporters.

Ko Wen-je, chairman of the Taiwan People's Party, was held overnight before the scheduled hearing.

Supporters gathered outside the prosecutor's office in Taipei, holding signs and chanting slogans demanding Ko's release and alleging judicial oppression.

Investigators refused Ko's request to return home out of concern he would collude with others involved in the case.

Ko, who trained as a doctor and also served as mayor of Taipei, and his TPP emerged as a third force in a sometimes rambunctious democracy dominated by the ruling Democratic Progressive Party and the remainder of the Nationalist Party that fled to Taiwan after the Communist Party's takeover of mainland China in 1949.

Ko and others were named in May in the scandal in which the developer of the downtown Core Pacific Center shopping center was given permission to massively expand the floor space available for lease during Ko's 2014-2022 term as mayor.

Ko's home and TPP offices were raided before he was called in for questioning on Friday.

The shopping center is still under construction, and DPP politicians have called for a suspension of work or even demolition.