Cho is accused of yelling at the ad firm manager and throwing a cup of water in his face at a business meeting last month. Police launched a preliminary investigation last week to decide whether to formally pursue the case.

Police questioned officials of the ad firm as reference witnesses Monday to cross-check arguments from both sides.

Cho, who had been overseas, returned home Sunday amid the mounting scandal. Later that day, she sent an email to all Korean Air employees to apologize for the incident, saying she will take all criticism to heart.

Cho has denied she threw the water and insists she only pushed him.

Public criticism has been intensifying against the owner family of Hanjin Group, the air carrier's parent company. Cho is the sister of Cho Hyun-ah, who was jailed in 2014 in the so-called nut rage scandal after she ordered her flight back to an airport gate in New York because she was upset about the way her nuts were served on the plane. (Yonhap)