Difficulty understanding the following sentence 穴？ 一体何を証拠に…

So usually when there is an omitted part of a sentence its pretty straightforward to know what the rest of the sentence way going to say. However in this case its really confusing me.

This is a scene from an anime where the person speaking is being accused of digging holes on a race track to prevent the other person from winning:

穴？ 一体何を証拠に…

Not only am I unsure of what the renaming part of the sentence could be, but the を particle is also throwing me off, something keeps irking me that it should be が.

I did some googling and 何が証拠になるのか seems to be a commonly reoccurring phrase, but nothing comes up with を.

Any help or clarification is much appreciated.