South Korean police said Monday it is investigating a 28-year-old man on suspicion of locking up his girlfriend at his home and threatening her, after she expressed her wish to end their romantic relationship.

According to Seoul Gwanak Police Station, the suspect is believed to have confined the victim in his home in Gwanak-gu, Seoul between 1 p.m. and 8 p.m. last Thursday. When the victim dumped the suspect, he became enraged and violent, throwing a soju bottle and threatening to hurt the victim with a knife.

He then forced the victim to take him to her former boyfriend, after threatening to kill him as well, but a passerby grew suspicious of their behavior and reported him to the police.

Investigators found that the suspect had psychologically tormented the victim for the three months they had dated. He is being investigated for illegal confinement and special intimidation, defined as intimidation by collective force or by using a weapon.