I posted (along with a million other people!) to ask when they think new cases might be added. Here was the response. I thought it was pretty cool!
Congratulations on finishing the first 20 cases. We will continue to release more case sets in the near future. The cases in Crime City are like CSI episodes you can play, and they are created with writers from the actual show who developed the stories, wrote the dialogue, and worked with game designers and artists to bring them to life as compelling, bite-sized interactive narratives. Because of this they take a while to produce and test! Thank you for your patience!