Locate the bookstore window that has the book on the Holy Grail. Look in the window next to the door to see Jane Jensen, the woman that developed the Gabriel Knight series of games. Additionally, examine the book that Gabriel authored about the Voodoo Murders. Gabriel will say "Wow, isn't he some famous author or something?".
Hint:-----
As with any adventure-game locale, look everywhere
that you can and talk to everyone. And if you can
pick something up, do so, because you will almost
certainly need it later, no matter what it is. Hint:-----
Learn to use the in-game camera function; not only
will Gabriel and Grace move more quickly around the
game's locales, but certain puzzles will be easier
to solve if you look around with the camera. Hint:-----
Once you get the fingerprint kit, you can look at or
inspect a suspect's inventory items, but don't pick
them up until you dust them for fingerprints. Hint:-----
Save the game after the first murder occurs. The game
will then shift into real time, and Gabriel can wander
around, talking to or spying on the suspects, but only
for five minutes. If you go back to the save point,
you'll be able to take Gabriel on a different route and
learn different things about the case. Hint:-----
On the game map, the Hint button tells you where you need
to go to finish a section of the game. But try to go to
every location, because you never know whom you might
bump into or what you might learn about the case.