You are gathered around the latest victim with your partner. This has been the fourth one this month, and yet you are no closer to solving the mystery. The victim is a history student, apparently lead into one of the janitorial closets and killed. The method isn't obvious and you are still waiting from a report from the morgue about any of the previous ones. Your partner notices something.
Look! There's a small slip of paper in the victim's hand!
Indeed there is. You take a closer look at it and discover it has a note on it. Maybe it is a crucial clue.
521b why how
It makes no sense. You can't see any meaning to this note. You consult your partner about the previous victims, trying to find a pattern.
The first victim was a computer scientist.
The second victim was a mathematician.
The third victim was a chemist.
The fourth victim, this one, was a historian.
There's no correlation, no motivation you can see that would connect them. You prepare to leave to mull over this information when you spot a note on the wall. Surely that wasn't there before. You would have noticed it earlier. It says:
This must be a clue! You take it from the wall and begin work on decrypting it.
What does the note say?
You ask what each of the victims were studying to get more insight into the killer's motives. The first victim was studying text encoding. The second victim was studying Fermat's last theorem. The third victim was studying atomic bonds. The last victim was studying secret communication in the 20th century.
Understanding how the victims relate to the note is essential to figuring out what encryption has been used.
Consider the order in which the victims were killed and the order in which something is encoded.