It doesn't seem to be possible to scroll through the journal using arrow keys or page up/down. The only way I could find to scroll through the journal was the old trick of highlighting some text and extending the selection past the end of the page.
Maybe I'm bad at this, but I had to deduce the culprit purely based off motive. I was able to determine the cause of death, but even after doing a second playthrough to check the things I originally skipped for lack of time I couldn't find any tangible evidence pointing to anyone, not even the "planted" evidence that presumably should point at the defendant.
In my second playthrough I decided to accuse someone else to see what would happen. The defendant being found innocent even though the real culprit was never found seemed like a nice consolation prize for at least having gotten the other questions right. But then I loaded a save created right at the end and found that I get the same ending no matter wrong I am. The game even lets me accuse the defendant of the murder, yet somehow this still results in the defendant being found innocent! As for the good ending, it seems that as long as I get the location and culprit correct it doesn't matter what I choose for the murder weapon.