1 Jane Doe was considered a witch
Back in the time of the Salem witch hunts, the girl was believed to be a witch and was tortured badly. Tommy believed that the girl was innocent and that she was tortured for nothing.
2 Jane Doe wanted revenge
Jane doe wanted revenge against people for the brutal way she was tortured. This is why she was making humans see things and suffer.
3 The hallucinations were created by Jane
All the hallucinations Tommy and Austin saw were created by Jane Doe in attempt to make them suffer.
4 Tommy decided to sacrifice himself
Tommy believed that if he sacrificed himself, Jane's desire for revenge will be quenched and the cycle will stop. Tommy whispered this to Jane and this is why she tortured him the same way she was tortured.
5 Austin killed his father
Austin killed his father in order to end his suffering after he realized he was tortured by Jane.
6 Jane killed Austin
Tommy's plan didn't work and Jane continued to seek revenge. She made Austin hear the voice of the sheriff while in fact it was another hallucination. Austin fell and broke his neck as a result.
7 The cycle might go on again
The ending of the movie opened the possibility for the cycle to be repeated again, as Jane's body was being moved to a different place.
8 Some suggest it was all in Austin's head
Some fans suggest that Jane was a normal corpse and that Austin imagined everything in order to find an excuse to kill people. Those people theorized that Austin was feeling guilty and that he was getting rid of it through hallucinations.