From 11:00PM PDT on Friday, July 1 until 5:00AM PDT on Saturday, July 2, the Shmoop engineering elves will be making tweaks and improvements to the site. That means Shmoop will be unavailable for use during that time. Thanks for your patience!
Dr. Robinson is, first and foremost, a murder victim; Injun Joe kills him in order to get back at Robinson's father, who apparently had Joe jailed for vagrancy. We also know that the doctor had enlisted the help of Injun Joe and Muff Potter to help him rob a grave, but we never find out why he needed a dead body.