Prosecutors on Friday summoned a former executive of Samsung Group's now-defunct Future Strategy Office regarding alleged improprieties behind the controversial 2015 merger of Samsung C&T and Cheil Industries.

The Seoul Central District Prosecutors' Office is questioning Kim Jong-joong, the former president of the group's decision-making body involved in the merger process as then chief of the office's strategy team.

Prosecutors suspect Samsung management intentionally lowered the value of Samsung C&T ahead of its merger with Cheil Industries to help benefit group heir and Samsung Electronics Vice Chair Lee Jae-yong in his managerial succession.

There's also suspicion the value of Cheil Industries, of which Lee held the largest stake of 23-point-two percent, was inflated ahead of the merger.

Through the merger, Lee was able to secure control of Samsung C&T, a de facto holding company of Samsung Group.

Earlier on Tuesday, prosecutors summoned former Samsung C&T CEO Kim Shin as a criminal suspect, but allowed him to leave early due to the status of his lawyer.