I did think about these being Bhaal cultists as it appears it is only 5 years (1482) till the last Bhaalspawn die and Bhaal is resurrected. Then the victims are either Bhaalspawn or murders to power a ritual and then that ties into the first 2 games. But the murdered dragonborn is almost certainly not a Bhaalspawn and there would likely be few left if the last 2 die in 5 years so I don't think this is the plot line but certainly can't rule out Bhaal cultists.
