Felice and Nicholas are the murderers. The numbers correspond to atomic numbers on the periodic table of elements: 'Fe-Li-Ce/Ni-Co-La-S'.
You look in the mirror and see what you saw. Take the saw, cut the table in half, two halves make a whole and you go out the hole.
The letter ‘x’. It is the 24th letter of the alphabet, XX in Roman numerals is 20, and XXX is a label for movies that are inappropriate (unclean).