The numbers 12, 4, 8 and 3 are written by Aleph. A few numbers are also circled.
Its fair to assume that the circled numbers refer to the letter present on that position of the month name and the written numbers define the sequence of the letters.
12 = December
5th letter of December = M
4 = April
4th letter of April = I
8 = August
6th letter of August = T
3 = March
4th and 5th letter of March = CH
Therefore, the name of the killer is MITCH.