From the original article:
"Mr. Martin was reportedly confused and refused to give a statement to the press."
Also, from the original article you can see Mr, Martin, nicley pressed shirt and trousers, stone-faced sitting calmly in a chair. Of course he wants to play the role of a confused and spooked old-fart. And so do the police want you to think that he is spooked and confused and, hence, the reason why they have not charged him. It is not in the best interests of the police to let the Thai justice system run its natural course while there is still time for money negotaition. There is a reaon why the police put in their report that "Ms. Savitree Seesun, 25, who (at time of accident) was offering food to a monk on the side of the road". They are going to put the screws on him when the negotiations start at the police station. I doubt very much that he will be charged with anything if he can come up with the money. Before you expat sympathsizers get your hump up, remember it could have been you crossing the street or driving your vehicle while this selfish $%$!! was crashing into you while trying to escape the police.