As all of tu know when Ben turned the frozen donkey wheel he was banished from the island and was moved 10 months in the future.
Then many theories were pointing to where did the island go well here's mine:
tu Can see in the promo that there were strange
people Carrying WW1 pistolas and WW1 Clothes [Correct me if I am wrong] then maybe the island moved 90 years in the past and to wherever the WW1 Took place .
Now... if that is correct then Ben is only trying to return to the island himself por convincing Jack that it happened "Because he Left" and he has to go back.
If I am Right Then he probably killed "Jeremy Bentham" to prevent him from Telling the truth.

This is my theory Don't forget the comentarios good o bad Don't forget it.