When Alicia enters the room go through the dialogs.
When the dialogs end, select the slide viewer from your inventory,
then select the 3 slides from your inventory one by one and they
will be inserted automatically inside the viewer.
After the dialogs put all three slides in the slide viewer.
This action will reveal a hidden passage among the bookshelves.
Enter the secret corridor...

Edit room:
When inside the edit room go to the table and go in close up.
Click the small square on the panel board and click the screen in
the middle.
It will start a movie showing Josef shooting at Constance.
Follow the dialog then click on the movie again and go in
investigation mode.
Get in the console again and click on the screen in the middle to
see the hero walking up the stairs in the church...
Get in the console again, and have a look at the movie again.
Find the "third" hand carrying the corpse in the investigation
close-up in the last frame of the movie.
After Jack enters the room follow the dialog and watch the end
sequence.