Reference for a proof of a projective representation of $A_6$

Question

I want to understand the proof of

There is a projective representation of $A_6 \hookrightarrow PSU(3).$

I am looking for a reference, but could not find. Suggestions are welcome.

EDIT: We have a central extension: $$0 \to C_3 \hookrightarrow \hat{A}_6 \twoheadrightarrow A_6 \to 0. $$ From a result of Schur, the determining the projective representation reduces to determining a linear representation from the central group extension $$\hat{A}_6 \to SU(3).$$ Now I don't know what the next step should be.

A reference will be very helpful to me.

Answer 1

One reference I found was

Solving the sextic by iteration: a study in complex geometry and dynamics by Scott Crass

I am just beginning to read this, so don't know yet how useful this paper will be to answer my question. So, if there are other suggestions, please let me know!

EDIT: Additional reference:

http://books.google.com.ar/books?id=lYMAg_Sj7hUC&lpg=PR9&pg=PA29#v=onepage&q&f=false