Death Bell 2

Death Bell 2 (2010) is a horror directed by Yoo Sun-dong rated 5.8/10.

A class of students stays at school for a camp in an elite study group to finesse theirs and the school's grades. Upon the first night, the swimming coach is found murdered. As the students try to figure out what happens, a voice informs them that if they don't figure the murder out, students will begin dying in quick succession.