To answer your first question: perhaps the bones were dug up because the killer intended to move the remains to a different location. Just for a recent example of this, Jacob Wetterling. The killer exhumed and moved his body at least once that he admitted too. The killer could have decided to move them because erosion was starting to reveal bones due to the grave being too shallow (this was the reason Jacob's killer gave for moving his body) or perhaps the land the bodies were buried on was about to be developed and the killer knew the bodies would be discovered, so he or she hastily moved them.
Regarding the second. It's not unusual for individual people to have medical specimens, they could have been acquired due to studies, theft or perhaps they were inherited. Sometimes those specimen's are stored or lost and then forgotten about. Back in college I was part of a team of forensic anthro students who received a huge donation of skeletal material from the son of a retired doctor. The doctor had boxes and boxes of human bones in his basement that no one knew about. When the guy died his son discovered them and donated them to my Anthropology dept so we could open an Osteology lab.
