Just because it may branch to different endings depending on your choices and stuff doesn't make it non-linear. You still follow a single line from start to finish for whatever ending you got, and the plot progresses in a linear fashion.
Non-linear games allow you to take on things in just about whatever order you choose, ignore elements, do extras, etc.
My question is why are you trying to prove it's *not* linear, as though linearity is a bad thing. It's a more story-driven game, and linearity suits it in order to tell a story. Linearity isn't *always* bad, and every single game doesn't have to be open world.
"How do I get rid of a Trojan Horse?" -Sailor_Kakashi "Leave it outside the gates of Troy overnight." -Davel23
I enjoyed it, but I used a guide to find the clues and answers to the interrogations as I went. I had tried to play it previously and hated it because it was damn near impossible to read peoples faces and the way evidence and clues connected didn't always make sense to me. It was pretty linear though, you just went from one crime to the next without really anything else of consequence to do. It had its faults, but I give it credit for trying new things and I would be open to a sequel if they could iron out some of its issues.
TC, perhaps an example of a non linear game would help you understand.
Take The Darkness for example.
It's a game where you have the main story and objectives related to it but you also have an entire city to explore using the subway system. You have side quests you can choose to take on or not. There also a bunch of nice little things like you can prank call people by dialing random numbers or watch TV where they have tons of footage of old TV shows recorded and an entire movie.
LA Noire you just have the main cases to finish and that's it.