Prosecutors on Tuesday questioned Samsung heir Lee Jae-yong over the top conglomerate's controversial merger of two of its affiliates five years ago.  

The Seoul Central District Prosecutors' Office said that Lee returned home at around 1:30 a.m. on Wednesday, 17 hours after he appeared for the questioning.

Prosecutors reportedly grilled the vice chairman of Samsung Electronics about his involvement in the alleged improprieties behind the 2015 merger of Samsung C&T and Cheil Industries, including if he ordered or received reports on it. 

Lee is said to have denied the allegations, claiming that he never ordered the moves or received those reports. 

The prosecution suspects Samsung management intentionally lowered the value of Samsung C&T while inflating that of Cheil Industries ahead of the merger, to help benefit the heir-apparent in his managerial succession.

Prosecutors also suspect that alleged accounting fraud at Cheil affiliate Samsung BioLogics helped facilitate the merger, which ultimately assisted Lee in overhauling the group's governance structure.