A famous chemist was found murdered in his own lab.
There was no evidence except for a piece of paper with the names of chemical substances on it, which he wrote right before he died.
The chemicals on the list were;
On the day he was murdered, the chemist had only 3 visitors: his wife Mary, his nephew Nicolas, and his friend Johnathan.
The police arrested the murderer right away.
How did they know who it was and why?