I don't think the plan was murder from the beginning...I think that came later, whether an argument over money happened, or something else, who knows at this point. But they would not be so bold on the videos, and approaching other people who would recognize or even know them, if they planned to find a victim for the purpose of killing. Maybe they refused to pay Jaren, or she refused to do something they asked. I also believe that the disposal (manner) of her body was a poor attempt to hide evidence, not ever imagining she would be found at all, much less so soon, tying them to being the last people she was seen with.