Prosecutors raided Samsung headquarters in Seoul on Tuesday over allegations that the conglomerate paid 2.8 million euros to Choi Soon-sil (US$1=W1,136).
Choi, President Park Geun-hye's confidante at the center of a massive influence-peddling scandal, allegedly took the money to buy a horse and equestrian facilities in Germany for her daughter Chung Yoo-ra.
Chang Choong-ki (62), head of Samsung's corporate strategy office, the group's de facto control tower, has been banned from leaving the country.
Prosecutors also raided the headquarters of the Korea Equestrian Federation, which is headed by a Samsung executive, and the Korea Racing Authority.
Samsung signed a consulting contract in September last year with Widec Sports, a company established by Choi in Germany, and paid it 2.8 million euros.
The money was intended to buy pure-bred horses and rent special vehicles to transport the animals to European competitions.
Samsung has claimed the aim was to nurture talented Korean equestrians for the 2020 Tokyo Olympics, but there seem to have been no candidates other than Chung herself, and it is unclear how talented she is.
Investigators want to know if Samsung gave the money to Choi as a bribe seeking to benefit from her ties to the president.
Prosecutors also plan to investigate other conglomerates that were allegedly pressured by Cheong Wa Dae to donate money to Choi's dubious Mir and K-Sports foundations.
Meanwhile, prosecutors have arrested Cha Eun-taek (47), a prominent advertising director who was a drinking buddy of Choi's and given a seat on the board of the Mir Foundation.
Cha was arrested on arrival at Incheon International Airport on Tuesday night.
Investigators leave Samsung headquarters after a raid in Seoul on Tuesday.