Here is the full list of all 21 The Infectious Madness of Doctor Dekker achievements worth 1,000 gamerscore.
Twenty questions - well done!
Ten responses revealed!
Two hours played
Fifty insanity points reached
One hundred questions asked!
One hundred responses revealed!
Two hundred insanity points reached
Two hundred and fifty questions asked!
Two hundred and fifty responses revealed!
Four hours played
Three hundred insanity points reached
Five hundred questions asked!
Solved the case using less than a hundred hints.
One thousand questions asked!
Five hundred responses revealed!
Eight hours played
Four hundred insanity points reached
Solved Doctor Dekker's murder.
Solved Doctor Dekker's murder without accusing any innocent people.
You made Nathan sing a song.
Zero hints, and you absolutely didn't cheat at all.