The Firemen determined that the fire was arson.
Officer Jung would never forget what happened two days before, he had no regrets. He was hoping that Jungkook had not killed anyone,that would be awful to take the man he loved to jail. Jungkook didn't even realize he didnt throw the shirt in the trash completely but he was scared and he needed somewhere new to hide. Hoseok had handed the evidence over to the crime lab knowing he could be arrested too but he had to know the truth. Yoongi however Killed Mark but wondered who killed the people on the train. More importantly, is he next?
All Yoongi knew is that he was being watched.

Jungkook sat underneath a bridge wondering why he had to be there on the train? Why his brother pushed him out so fast..however he realized Mark was gone forever. He'd go home and change but he couldn't risk being seen again. At headquarters it was discovered that the blood belonged to Jungkook,but Hoseok was to be questioned about Jungkook whereabouts. Someone was lurking in the shadows waiting for the deal to come through. He did not like to wait. But Yoongi had stall his best or his family could get hurt or worse die. Marks last thoughts were of Jungkook and Bambbam and that he should've told them what he did days before.

Mark knew he was going to hell,but it was either him or them. It was easer to kill them because they were complete strangers.
No one he thought he
knew of.
Yoongi should've made a different choice and let Bambbam die instead he stole the money and sent him away. Now Jungkook and Hoseok were in danger, Jungkook shouldn't have been on that train.
Hopefully Hoseok would be found guilty of stabbing his lover and not the big guy. Meanwhile Yoongi got a call from Jimin,repeating the words 'the big guy found out about everything'.