The independent counsel questioned two high-level executives from Samsung Group on Monday -- Jang Choong-gi , the head of Samsung's Future Strategy Office, and its deputy head, Choi Ji-sung .
Samsung's Future Strategy Office is the tech giant's control tower.
It faces allegations that it funneled money to President Park's confidante Choi Soon-sil in exchange for help with a critical merger of Samsung affiliates in 2015.
While both men were summoned as witnesses, the independent counsel remains open to the possibility of changing their status to suspects.
With the executives being called in, speculation is mounting that Samsung heir apparent Lee Jae-yong could also be summoned soon.
Choi Soon-sil, the main figure in the scandal, has been summoned for questioning, but she has again refused to appear, this time saying she needs to prepare for the impeachment trial at the Constitutional Court.
Meanwhile, the independent counsel team is seeking the arrest of people linked to a blacklist of cultural figures deemed critical of the government.
"The independent counsel considers the matter of high-ranking government officials enforcing such a blacklist as a serious infringement of the right to free expression and will hold those who created and administered the list legally responsible."
During the team's afternoon briefing, spokesperson Lee Kyu-chul named four people under investigation for abuse of power -- former Culture Minister Kim Jong-deok, former First Vice Culture Minister Chung Kwan-joo and two former presidential aides, Kim Sang-yule and Shin Dong-churl.
The probe into the corruption scandal is likely to only intensify as the independent counsel digs deeper into the roles of a range of figures in and outside of the government."
Hwang Hojun, Arirang News.