While the team of independent counsel Park Young-soo is poised to question President Park Geun-hye later this week, investigators are closing in on another key target of their probe, Woo Byung-woo.

The team questioned Saturday the owner of a major gallery about Woo’s purchases of high-priced paintings. Investigators also summoned a police officer for the second time Sunday in connection with allegations that Woo exerted influence to secure a personnel-related favor for his son, who was serving his mandatory military service in a police unit.

There is no doubt that investigators should shed light on these two allegations as well, but it would not be wrong to say that they pale in comparison to other major suspicions surrounding the man who held the powerful post of senior presidential secretary for civil affairs until October.

Most of all, Woo cannot avoid responsibility for failing to check Park and her civilian confidante Choi Soon-sil from abusing their power and peddling influence, which is the prime cause of the scandal that led to the president’s impeachment and months of political mayhem.

One of the senior secretary’s most important jobs is to monitor people close to the president -- relatives, friends and associates -- and keep them from abusing their ties with the chief executive for personal gain.

Choi maintained close ties with Park from the 1970s and their relationship became even closer after Park was elected president. That emboldened a woman who had no official title to interfere with presidential and state affairs, with the president providing personal assistance in many cases.

Given what has come to the fore so far, it is hard to believe that Woo and his office, which was supposed to constantly watch the president and those around her, had not known what Park and Choi were doing. In this sense, Woo should be put below only Park and Choi on the list of people to be held accountable for the scandal and the ensuing national crisis.

That is why the special prosecutor’s act included suspicions surrounding Woo as matters subject to its investigation. In other words, much of the success of the team’s investigation will hinge upon how thoroughly it can probe allegations related to Woo.

One of the top priorities of the investigation should be on the allegation that Woo interfered with the inquiry by Inspector General Lee Seok-su, who was fired by Park last year in the middle of an investigation into some of the allegations connected with Choi. Lee also was looking into the allegation about Woo’s son.

Taking disciplinary action and vetting of candidates for senior government officials, including those named by the president, are also main duties of the senior secretary for civil affairs. Woo is suspected of abusing this authority as well.

The independent counsel team, which has already taken custody of former presidential chief of staff Kim Ki-choon and former Culture Minister Cho Yoon-sun on charges of blacklisting artists and cultural figures, suspects that Woo played a part in the case. Woo is alleged to have pressured the Culture Ministry to transfer five officials to posts outside the ministry.

Then came the allegation that Woo’s office was involved in the replacement of the ambassador to Myanmar. Investigators suspect that Park named a former Samsung executive as the new envoy to Myanmar last year at the request of Choi, who was pushing business projects there. The ambassador, Yoo Jae-kyung, told investigators he was named to the post with the help of Choi.

All these and other allegations raised against Woo require the special prosecutor’s team to leave no stone unturned. That’s no easy job, however, judging from what we saw during the state prosecution’s investigation of Woo.

Having been a link between Park and the prosecution, Woo, himself a former senior prosecutor, has deep connections to senior prosecutors, which is believed to have helped him avoid indictment by state prosecutors when they looked into some allegations. The same concern lingers on even with the independent counsel team, which also includes former and incumbent prosecutors who are close to Woo. Special prosecutor Park should make sure any such worry is unfounded.