User blog comment:Doobie Wah/Jojolion Part 8 theories/@comment-1739368-20150729172615/@comment-26781310-20150730164342

Simple, Jobin has a stand that can kill people without leaving a trace on the body and Yoshikage Kira didn't die of health problems.

In addition Kira most likley knew that Jobin was allied with the rock humans, due to the ammount of fruit trees Kira collected/almost disposed of (weither or not this was on the orders of Noriuske the fourth is yet to be seen), so Jobin had to keep him quiet.