> I admit the driver did something wrong and was to blame, but how do the
> authorities know he fell asleep at the wheel.?

Is that a question or a statement? I can't tell with your constant use
of both a period and a question mark.

Perhaps you need to read up:

http://en.wikipedia.org/wiki/Question_mark

A question mark (or, less commonly, an interrogation point) is a
punctuation mark that REPLACES the period at the end of an
interrogative sentence.