The independent counsel team on Sunday asked a Seoul court to issue an arrest warrant for ex-presidential secretary for civil affairs, Woo Byung-woo, Sunday, for his role in the influence-peddling scandal involving impeached President Park Geun-hye and her confidant Choi Soon-sil.
The move came a day after investigators summoned him for questioning.
Woo, 50, returned home Sunday after being questioned for 19 hours on charges of abuse of power and negligence of duty.
The counsel team now has one week left to complete the investigation.
Walking out of the special prosecutors' office in southern Seoul, at 4:44 a.m., Woo told reporters: "I sincerely answered all the questions."
Asked if he received favors from Choi to become presidential secretary for civil affairs, Woo said, "That is not true." He made no further comment.
The prime charges against Woo are that he overlooked or abetted Choi, who did not hold a government post, in meddling in state affairs. He also faces charges of interfering with former presidential inspector Lee Seok-soo's investigation into the Mir and K-Sports foundations controlled by Choi, and exerting influence to get him dismissed.
The investigation team, led by special prosecutor Park Young-soo, reportedly focused on examining those charges in the night-long interrogation.
The team said it had already secured circumstantial evidence that Woo involved himself in the culture ministry's personnel affairs. Five anonymous culture ministry officials testified that Woo had them demoted to ministry-affiliated agencies last year because they had refused to comply with illicit instructions from the ministry.
Woo denied all the allegations, stressing that he had never met Choi.
After checking records related to Woo from the prosecution's special investigation team that previously looked into his case, the team is also investigating alleged personal corruption, including embezzling money from a family-run company and using his influence to get his son an easy post during his compulsory military service.