There are 5 endings.
3 "bad" endings.
1 "good" ending.
1 "true" ending.
The good ending requires:
You talk to Kokomui, check the tray, find the phial, talk to Hitchcock to get the glass and find the empty Sabotender suit. These will all open up new dialog choices and allow you to point to Kokomui as the actual murderer.
The true ending requires:
Finding all the clues for the "good ending" and also the parchment scrap. The parchment scrap will open up a final dialog option that will reveal the full truth of the events and a cutscene with a visit from a special guest.