I am trying to speculate about where the perp was going. Let's assume for a second that it accidentally fell off the back of a pickup truck (instead of being intentionally dumped from any kind of vehicle). Looking at the location of the tarp, if it fell off the back of a pickup right there, then it seems like it must have been driving eastward (upwards in the picture) on Roundrock Drive. But, looking at a map of the area, it's hard for me to see why anyone would be doing that. It's not coming from the direction of Alanna's neighborhood and it doesn't go anywhere useful.
A few people have wondered up thread if the original location of the tarp may have been the cone shown in the picture (and perhaps the tarp was moved by the boys who discovered the body, after they first dragged it out of the middle of the street). Descriptions that the tarp was found " in the middle of a quiet intersection" seem to support that idea (though perhaps the pictured location of the tarp seemed close enough to the reporter to describe it as the middle of an intersection).
If the cone is the actually location the body was found, that opens up different possibilities for where the perp was driving when the body fell off the back of the truck (again, assuming it happened that way). Perhaps the truck had come down Woodcrest Drive, taking back roads from Alannah's neighborhood. The right turn from Woodcrest onto Roundrock (westward) is pretty sharp. The body might have rolled into a less stable position. Then when the truck took the first subsequent turn on Cindy Lane, it might have tumbled out.
So,possibly, the truck driver was taking back roads away from Alannah's neighborhood, threading to the south somewhere. I have no idea where it would be headed, but at least the route make a little more sense that way to me (heading westward on Roundrock instead of eastward).