So the MC is the murderer and purposely wrongfully accused the ML's older brother. Don't t...

Right. I'm impressed I also did not see this coming.

Nooo! It was the ML's father that "supposedly" committed the murder. The ML's older brother only tried to cover it up by accusing the MC of it, and his entire family tried to frame the MC for the murder. Unknown to them, after the father hit the victim, he survived it and the MC was the one that dealt the final blow, after all.

I'm so curious to know the reason behind why he killed the victim.

Remember that scar on his stomach? It was the victim that did it. From his flashbacks, it seems his Dad owned a butcher shop and gangsters were always tricking them. I can't understand the translations very well but it's like they killed his father in the bathroom and the victim was the one that entered the MC's bedroom to kill him by slashing his stomach but the MC survived it.

It also seems like the MC killed off all the gangsters and was only left with the victim who escaped. He traced him to the town and that was why he told the victim "Thanks to you, I moved here," and then proceeded to finish him off too. The ML's elder brother saying that he saw him kill the victim was most likely a lie because he didn't know. He just knew that the MC had gone to jail for murder before and wanted to pin that one on him to save his father. Or maybe he didn't really spend time in jail for the previous murders so he felt he should go to jail for this one to pay for the previous ones. Unknown to all of them though, the MC was truly the murderer.

Honestly, the translations at the end are shitty and I started reading this a long time ago so most of the information is lost on me. I might have to read it again to fully understand some part of that plot. But the reason why he killed the victim as I explained is clear in the last chapter.