I am pretty sure this is korean webtoon

A homeless man was always sit in front of the school entrance

Police already arrested him but found out he never do anything dangerous so he got released.

Even so the homeless man still going back to school entrance and sit there.

The parents are worried but the police say he wont do any harm, so the school put a cctv camera near the school entrance to monitor the homeless man.

The highschool boys seems to treat the man like bum and laughing at him while the girl avoid him because he was scary.

The mc was a boy in high school along with his childhood friend a girl, the boy dislike the man because he always see the childhood girl with perverted look.

One day it was raining and the boy see the homeless man walking to an abandoned warehouse and the boy did not interested on it and left him alone.

Next day the childhood girl die.....her body been found out in the warehouse and she also got raped.

The boy was so mad and crying, regreting why he did not follow that homeless man and i think some supernatural thing happened like time reverted ?? I kinda forget.