The fourth and final suspect behind the narcotics scheme in Gangnam-gu, Seoul, was arrested Thursday in Daegu, according to Seoul Metropolitan Police Agency.

The offender is currently being questioned for charges of violating the Narcotics Control Act.

On Wednesday, a woman in her 40s was arrested for offering high school students drug-infused drinks, claiming that they would increase their ability to concentrate.

The incident happened in Daechi-dong, Gangnam-gu, which is also the country’s premier district for private education.

An accelerated police investigation was conducted and was later revealed that the suspect had approached various students on the street with three other accomplices.

Officers say the suspects also blackmailed the parents of the students who consumed the drink.

After asking the teenagers for their parents' numbers to "check purchasing decisions," the culprits threatened the parents that they would report to police the students have abused drugs in exchange for money.

The police are probing this case further as they suspect that there is another person in charge behind the four suspects who planned the crime.