Thank you for the compliments!
Spoiler: The goal is to figure it out yourself but you're supposed to find the Patient Zero, also known as the one that spreads the disease, and trap him, saving as many souls as possible in the process. This means that you should try to trap only the Patient Zero which is rather hard because you have to find him first, and it is difficult to be correct on your first try.
The Patient Zero is the only one, in this case, that spreads it. How you find him is up to you to discover, it has been answered already in other comments.
Thanks for playing.