To unlock the following, you have to play the game and collect/Earn achievements. You can find those earned achievements in your Game-Main menu or you can view them if you signup at one of the Steam communities.
Unlockable: --- How to Unlock:
A Complex Mind (70 GP) --- Reach all possible conclusions in the game.
A Deadly Flower (15 GP) ---
case. Finish Kew Gardens
A Man of Character (70 GP) --- Receive maximum personality ranking.
A Methodical Man (70 GP) --- Gather 26 Character Portraits.
An Omnivorous Reader (30 GP) --- Receive 3 messages from those whom you condemned or absolved.
Aye Aye, Captain! (15 GP) --- Finish Black Peter case.
Blood and Ice (15 GP) --- Finish Blood Bath case.
Bruiser (30 GP) --- Beat Cairns in a fight.
Child's Play! (30 GP) --- Finish 25 mini games and puzzles without skipping.
Dog-fancier (30 GP) --- Interact with Toby in every case.
Elementary! (30 GP) --- Finish 35 mini games and puzzles without skipping.
Guilty Brotherhood (15 GP) --- Finish Half Moon case.
Haunted House (30 GP) --- Catch the thieves at Notting Hill Manor.
Hold your Herrings, Captain! (30 GP) --- Save Crocker from committing suicide.
I Never Fail (70 GP) --- Finish 10 Dialogue QTEs without a failure.
I Never Guess (70 GP) --- Reach 6 correct conclusions for all 6 cases.
Keen Observer (30 GP) --- Finish 15 "Character Observations" without skipping.
My Grey Matters (70 GP) --- Finish 45 mini games and puzzles without skipping.
Off the Rails! (15 GP) --- Finish Train case.
Perfectionist (130 GP) --- Collect all possible in-game achievements.
Raider of the Tombs (30 GP) --- Retrieve the Golden Knife from the ancient
. temple of Mithras
Sharpshooter (30 GP) --- Disarm Mexican by shooting the gun from his hand.
Suicide is Not an Option! (30 GP) --- Prevent Miss White from suicide.
Their Crimes, Your Punishments (30 GP) --- Complete the game.
Vox populi, vox Dei (15 GP) --- Finish Abbey Grange case.