How did the DA know...?

The DA followed the 3 in the car. As he was quite a ways behind them, how did he know they would make the impromptu left turn and take the 'scenic route' ? I say the DA was far behind as he didn't arrive at the crash scene until well after the scene in which Frank and Nick got out and tested the 'echo', the time delay when Frank needed a few seconds to build up his nerve to whack Nick with the bottle, roll the car over the cliff, climb down and deal once again with the car/Nick and then the time it took Cora to climb back up to the road. If the DA was traveling even at only 40mph, this would indicate he was at least a mile behind them. So, he could never have been close enough to see them make that left turn and would have no reason to think they would. I guess its possible to assume the time was wasted by the DA, in an attempt to catch up with them, drove right by the road on the left and realized when they didn't come into view that they must have turned somewhere and he doubled back after them, guessing at the road they took. Hmmmmm.... possible..or a bonafied 'Continuity'/'Goof' ?