By Chyung Eun-ju, Park Si-soo

The Supreme Court has confirmed life imprisonment for a woman who killed her married lover's wife with poison. The top court upheld an appellate court's verdict.

According to court documents, the woman, Han, 48, met Yoo, a married man who became her lover, at a gathering of friends from elementary school in February 2014.

Han told Yoo's wife of their "deep and serious" relationship, hoping this would lead to the couple's breakup. But instead Yoo's wife offered to pay Han 350 million won ($309,700) if she ended the relationship.

In January 2015, Han visited Yoo's apartment in Songpa-gu, Seoul, with a bottle of soju mixed with potassium cyanide. Yoo's wife drank the toxic liquid while talking with Han, and died soon after.

Han claimed Yoo's husband could have killed his wife.

But investigators found evidence that Han collected information about how and where to buy potassium cyanide.

They also found evidence that her husband was informed of the poisoning plan before hand.

"Lee (the late wife) tried to keep her family together despite knowing about the affair by giving 350 million won to Han and even left a note saying she would live a happy life for her daughter," said the court. "She could not have impulsively committed suicide."

The court added that when the husband found his wife dead at home, he calmly phoned Han to talk about it.

"The phone call was made only six minutes after he returned home," the court said. "Six minutes is not long enough for a person to die after drinking the toxic cocktail."