Just a couple of thoughts:
-if this was someone who had abducted/killed before, and Alanna's body was intentionally left in the street, it could suggest that they like the attention their crime gets. If a body is found straight away, they not only get gratification from the abduction/murder, but also a sense of pride/fulfilment from the media attention. If a body is not found straight away, they have to wait for this second wave of satisfaction.
-the lack of clothing COULD suggest that the murderer wanted to dispose of them separately, maybe due to fear of their DNA been found on clothing? Leaving the underwear on would suggest some level of empathy - not removing them gives her at least some sense of modesty. This would also suggest no sexual assault. In this case, it could indicate an accidental murder
-if Alanna fell out of the truck (or another vehicle) accidently, the murderer would be extremely agitated and feeling a lack of control afterwards. Could you imagine the person arriving at the chosen disposal location and there was no body - anyone close to that person would likely notice a real obsession with the case, trying to find out if and where a body was found, etc. This would probably apply if it was accidental or intentional killing.
-I would like to know more detail on how Alanna was tied up (I have been trying to keep up with posts, so not sure if it's been officially released yet). Tying a body up could have a number of purposes - as a restraint when Alanna was alive or maybe to aid in disposal.
-I am thinking whoever hurt Alanna had somewhere to do it (regardless of whether her death was accidental or intentional). They couldn't just pull over in broad daylight and secure her body with tape, belt, tarp, etc. This would have to have happened either in a home or a deserted area, where privacy was essential. For the sake of TOS, let's assume the family is not involved - this means whoever killed Alanna had somewhere to take her before transporting her near to where her body was found.
I'm only an amateur sleuther but these are just some things that jumped out at me
Bless Alanna's little heart.