What happens when you mix carbon, oxygen, nickel, lanthanum, and sulfur?

This is one of the 7 mystery crime riddles. This is where a famous chemist was found dead in the laboratory and the murderer left a paper with these 5 elements. There are three persons who visited him that day, Mary, Nicolas and a friend named Jonathan. On that day the police arrested the murderer and it was Nicolas because on the elements written Ni is for nickel, C for carbon, O is for Oxygen, La for Lanthanum, and S for sulfur.