I'm not sure how to do spoiler tags on here, so warning for spoilers.
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SPOILER ALERT! SPOILER ALERT! PLEASE STOP READING IF YOU DON'T WANNA BE SPOILED!
Ok...hopefully that is good enough. As a big hint, I would say think about who has a motive to kill. Who has power in MAN-ticore, and also who would have had a reason to kill Timmy?
If you're still struggling, then the answer is that the killers are Soren, Jon, John, Hunter, and Abzi, I don't know if there's a super obvious way to figure it out, but I just thought about the reactions to the different people. Soren was super apathetic to Timmy dying, and he also held a grudge because he felt Timmy got past him to Tad. Soren is also hinted at to be the most powerful person at MAN-ticore and he's the heir of the company. Jon and John are kind of obvious... I mean they give death glares to anyone who challenges their position and they're also violent. Hunter is tricky, but you can get scenes with him where he basically reveals he has a survival of the fittest mentality. He only cares about strength. And Abzi not only has the most to lose when rising stars appear, but there's also some hints here and there about him being very brutal (not to mention that creepy painting in his house).
After you get past that hurdle, you'll also face a series of puzzles. If you need hints or answers, then here's some help. For the first one, it's an algebra problem, using substitution. Treat the symbols, like x, y's, and z's. The ending amount is 154.5. The next one, I would focus on the riddle - the answer is ONE. And the last one, the hints mention Greek gods. It's an eight letter word with no numbers. Also the plaque says "only through him shall you find release." if you use the letters given, then it will lead you to Thanatos, the god of death.
This will lead you to ending four, the "beautiful" ending. I'm assuming it's the true ending, but I'm still trying to unlock the other endings, so I can't say for sure.