Mani, I suspect, for the following reasons, that Allison was dropped from the bridge:
(a) the creek from the scout camp seems to be very minor and untraffickable; it seems incongrous that the body would stop travelling down the creek under the bridge at the very point where the water becomes deeper and wider;
(b) driving around with a body in the car is relatively safe; stopping for a minute on a bridge at night also seems relatively safe; dragging or carrying a body around at night through the scrub in the darkness or with a torch, away from one's car risking injury and trace evidence is fraught with risks that a perpetrator would probably try to avoid;
(c) A bridge is probably the only place that is convenient that a body can be dropped from the road with the expectation that it won't immediately be found. It is convenient because it takes away the risk of dirtying shoes and clothing, scratching shins, leaving a trail of evidence behind eg. shoe prints etc and introducing evidence into the car/s.
MOO :cow: