Murder Calendar

A man is found murdered in his office. The suspects are Anna, Nina, Jason and Lee. The only clue is a set of numbers written by the victim on a calendar with his blood. The numbers are 1,4, 9, 10 and 11. Who is the killer?

Answer

The numbers written on the calendar actually represents the months in the calendar whose initial letter represents the name of the killer.

1 = January [J]
4 = April [A]
9 = September [S]
10 = October [O]
11 = November [N]

The killer is Jason.