Here is the full list of all 19 Murder Mystery Machine achievements.
Complete Episode 2
Complete Episode 1
Achieve an A+ Grade on Episode 1
Pass the Tutorial
Achieve an A+ Grade on Episode 2
Complete Episode 3
Achieve an A+ Grade on Episode 3
Complete Episode 4
Achieve an A+ Grade on Episode 4
Complete Episode 5
Achieve an A+ Grade on Episode 5
Complete Episode 6
Achieve an A+ Grade on Episode 6
Complete Episode 7
Achieve an A+ Grade on Episode 7
Complete Episode 8
Achieve an A+ Grade on Episode 8
Unlock all outfits for Cass
Unlock all outfits for Nate