Ahn Jong-beom is the second person detained in connection with a scandal that has plunged Park's approval rating to record lows and triggered mounting calls for her resignation.
Earlier this week, prosecutors detained Park's friend, Choi Soon-sil, and requested an arrest warrant for her.
South Korean media speculate Choi, who has no government position, secretly made policy recommendations for Park and pushed businesses to donate millions of dollars to two foundations she controlled.
Park may survive what has become the worse patch of an already rocky four years in office, but a major test will be whether opposition parties reject her recent nomination for a new prime minister. If she's forced to name a prime minster chosen by the opposition, it would hamstring her authority and might end her ability to govern.
Also Read
Prosecutors investigating the scandal detained Ahn on Wednesday night after they summoned him for questioning over whether he was involved in extracting USD 70 million in donations, according to the Seoul Central District Prosecutors' Office.
Ahn was among the eight presidential advisers fired by Park in an attempt to regain public trust in the wake of the scandal. Today, Park nominated a new prime minister and two other top officials, but opposition lawmakers quickly criticized the reshuffling as a diversion.
Much of the public frenzy over the scandal is associated with Choi's family background. Her father led a religious cult and reportedly was a private mentor for Park, whose parents each were assassinated in the 1970s. Park's father was a military dictator who ruled South Korea for 18 years.
A Seoul court will likely determine by Friday morning whether to approve an arrest warrant for Choi.
Disclaimer: No Business Standard Journalist was involved in creation of this content