They don't HAVE to tell their sponsors, but it would make business sense to know in advance how such a controversial move would be received by them.
Or they could just do it, and be 'surprised' when sponsors pull out in response.
What if the only reason he protests his innocence is to keep his girlfriend and her family onside? Will there be a time that he realises the game is up ? ???
I do wonder how long Evan's girlfriend and her family will continue to support him once he finally realises the game is up, and he drops his innocence protestations.
Also, it is the same director who brought in Lee Hughes to Oldham who admitted his guilt.