Special cases like The Chess Killer or The Dark Side of The Law are time-limited challenges, and they will be considered seasonal events. They will show up in your game after reaching some milestones in your law firm. If you didn't get them, NO WORRIES! All players will have the opportunity of playing the special cases. They will definitely show up when your law firm is ready.  

Would you like more seasonal cases? Don't worry! The team is actively working on adding more content. They want you to go to the court again! :P