My feeling is that the perp(s) didn't care whether the bodies were found or not. JMO. That fits in with my theory that the abduction/murder of these two little girls was a means to an end, not necessarily sexual in nature. Once the desired end was achieved, I feel the perp(s) didn't care one way or the other what happened.
This is based on nothing said by LE, or in MSM, or even (heaven forbid) stated on NG or JVM. Just my opinion and subject to change without notice!
If he didn't care, they would have been left in the ditch next to the dead end road, not in a depression next to a desolate spot near the river.