Nice game you got there! I really loved the integration of pixelated graphics with a 3d environment. The sound design was awesome, and the concept was also cool. As such, after finishing it once, I restarted the game, and found that the killer stays the same!
I feel that for such a short game (just a little over two minutes), there should be at least some replay value. Maybe make a randomly generated list of messages the people on the train give, and give the suspicious ones to a randomly chosen killer.
I also wasn't sure after completing the game if I had gotten the killer right or not- it simply flashed a news article saying "Murder on (some) train". The murder happened nevertheless of whether or not I found the killer, and therefore the article title would've been the same had I gotten the wrong person, right? Maybe put some text in the bottom that says, "You found the killer!" when one wins.
Oh, and in the start, it says "RMB to question" and "LMB to rewind". However, in the actual game, it's the opposite! I wasted the first minute just trying to figure out why I couldn't question anybody.
All in all though, this is a super interesting and fun concept! This could legitimately be a full game if it was extended moderately, and the puzzles were (somewhat) procedural! I can imagine this being a game on Steam where you play as an amateur detective :) Good job!