Police are conducting a school violence survey at a middle school attended by four students who were arrested in connection to their schoolmate’s death.

Incheon Yeonsu Police Station said they began surveying students Tuesday, with the cooperation of the Incheon Metropolitan City Office of Education, to discover other possible cases of violence inside the school.

Police have also discovered a record of bullying by one of the arrested teenagers in relation to another assault case earlier this year. 

In the course of the investigation, authorities also found the victim had been on academic probation, having missed more than one-third of school days this year.

The city’s education office announced it would on Thursday issue a statement concerning the death of the student and measures to prevent further school violence.

Last week, four teenagers were arrested on suspicions of causing death from bodily injuries after their classmate fell from the roof of a 15-story apartment building.

The teenagers were later pressed with additional charges of extortion and injury for physically bullying and taking by force the victim’s electronic cigarette. Police had found evidence of two of the accused students planning the assault on social media.

Authorities are also mulling additional charges on one of the four students for the possible extortion of the victim’s jacket, which the accused boy was seen wearing on his way to court last week. The beige jacket caused a public uproar after a person claiming to be the mother of the victim left a comment on a related online article claiming the jacket belonged to her son. The jacket has been confiscated by police and is to be returned to the victim’s mother.

Police said the teenagers asserted they had not forcefully taken the jacket from the victim, but that the classmates had exchanged their clothing. The teenager could face an additional charge of theft if there is evidence of coercion in the exchange, police added.

By Choi Ji-won(jwchoikr@heraldcorp.com)