I do think it was a murder also, and I think in the modern day it might be Kim Tae Sung that is part of the case to solve it. Might be a stretch, however his father is a police officer, and they took the time to show us that. Meaning that maybe, although a rowdy kid, he grew up to follow his father's footsteps and become a cop as well.
Just throwing darts here...I haven't read the webtoon, just found it was one by this thread.
I don't think InHyuk is involved in any of the nastiness. Maybe it is cause I don't want him to be, but I'm just not getting the groundwork lain for that. I feel like he is blaming himself in the present since he was giving Soen Jae so much grief and his fans were the one's attacking Soen Jae. Thus, he thinks he died because of him.
As for the wreck in the past, I am worried it might have been caused by Soen Jae...he was there to save her, and that grief that an accident he was a part of crippled the girl he was longing for is one of the reasons he was having so much trouble in the current day. And he still longs for her even though he knows he caused her pain. THAT would be a twist that punches the gut. And huge hurtle for their love considering so much has happened so fast in the show. Something major has to throw a wrench in this romance.
It might be the guy from the swim team that is Seon Jae's rival. And he was aiming to hurt Seon Jae but hurt her instead....which Seon Jae will also blame himself for, and also give a reason for him being there to save her....who knows.
Also, my bet is on the CEO as the killer if that is where this story goes......of course we are only 1/4th of the way through this, so things could change.
Oof what if Kim Tae Sung is part of the crippling accident...brain just winding away here...