At this point the circumstantial evidence is piled pretty high against the CA.

I proposed theories involving fires in the early days, even when many were quick to blame the CA (boeing has a long history of fabricating pilot love triangle suicide fantasies to cover up fatal design flaws).

But after years of analysis the digital forensics are pretty damning, even though it's circumstantial. The airplane flew a course, with several turns, which appeared designed to straddle airspace boundaries to avoid military interdiction and create ATC confusion. It's also reported that the CA executed the same profile on his home flight sim shortly before the flight... and then fast forwared to the middle of the IO. If everything reported in that youtube video is accurate, then it's fairly obvious what happened.

But I haven't heard of a plausible motive yet, so there's that.

And yes it is in the IO. Physics don't lie and that's where the SATCOM emissions say he ended up.