A student attending Korea University was arrested on charges of murdering his former girlfriend after she refused to date him again, police said Tuesday.

According to Seoul Seongbuk Police Station, the 20-year-old suspect surnamed Lee was arrested Thursday after he admitted to killing the victim ― another student at Korea University ― at her boarding house on Dec. 7.

According to the investigators, Lee ― who had been stalking the victim for months after breaking up with her last year ― forced his way into her room. When she shouted, “Get out or I’ll scream,” the suspect allegedly strangled the victim to death.

The murder, Lee claimed, had been out of impulse.

After the crime, Lee allegedly wrapped the electrical cord of the victim’s cellphone charger around her neck and covered the body with a blanket in an attempt to disguise it as a suicide.

Police, however, found no motive for suicide and suspected foul play. While the autopsy provided no evidence of murder, investigators found DNA matching Lee’s under her fingernails.

Police had grown to suspect Lee because of his relationship with the deceased. Police took Lee into custody on March 2.

During the investigation, police also found a self-portrait of Lee on his phone, taken after the day of murder. The photo showed he had scratch marks on his neck, which police suspect came from the scuffle with the victim.

Further investigation found that Lee was a repeat offender of physical violence against women; he was booked by police in 2012 on charges of assaulting and strangling his then-girlfriend.

Lee admitted to the charges and the police forwarded the case to prosecutors on Thursday.

By Yoon Min-sik (minsikyoon@heraldcorp.com)