I think moving the bodies or disposing can change based on situation. Maybe if something about the location of the abduction or murder will lead more directly to the perp, he will move or try to hide the body/bodies, or if the location of the actual murder is a van or a home where obviously you cannot leave a corpse. but method of disposal can still be the same where the method of abduction/or victim location at the time is different. yet the body is still...
out in the open
rural
under leaves and branches or refuse.
maybe leaving the body out in the open is an escalation and provocation. mOO
Okay, so I think what you're saying is that maybe circumstances change or circumstances may be different than an offender may expect. Certainly we also know that for these criminals, unfortunately they do increase in skill/experience as they commit crimes and some do become better at what they do, thus changing their methodology (others may be one more sloppy).
Having said that, everything that the FBI has studied leads them to think that method of disposal 1. Strongly correlates to factors about the criminal that point to his identity, so much so that it's a major factor in case resolution; and 2. Correlates strongly enough to offender method that it can be used to analyze linkage between murders in a series. So for me I give a lot of weight to what the FBI teaches investigators in this respect.
Consider that most offenders of this type are relatively opportunistic in what they do. They travel through certain areas that are familiar to them and they've already considered who might be vulnerable, how they might take a victim for their purposes. Maybe they've fantasized about a victim of this particular age or this specific type, but when it comes down to it they often decide who to victimize based on the best opportunity to do it undetected.
So the exact age of victim, for example, may be somewhat out of the offender's control. But what he does with the body afterwards, that's usually something he has more time to consider, to actually weigh what would be more or less risky. And I think, based on my research - it's just my opinion - that most criminals don't decide what to do with the body randomly. Not all - but most will stick to what they know or what they've rationally decided makes the most sense. There might be slight variations but for serial offenders I believe there will usually be a pattern.
The good news is that when they do switch things up, perhaps for expedience, I feel like it sometimes leads to them finally being caught. When they change things about their M.O. it's usually not a "so what if this is different this time" situation, there's usually a reason and it often points to their identity.