in the film Jill read Julia's journal to John. It said It's dark. can't see. jill where are you?. I believe Landis fooled Julia into going back to her apartment and he shot her in the head.
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At first I thought that Julia might have just gone back to her apartment for something she really wanted for comfort maybe....like a favorite book. Or that she felt angry that this nutcase was ruling her life, so she went back out of rebellion and courage.
But perhaps Landis impersonated John or even Jill's voice and lured her back, agreed.
I also think he wrote that journal entry himself.
"Some laughed. He let them. His own heart laughed, and that was enough."
-A Christmas Carol
it wouldn't surprise me if Landis wrote the journal entry himself. He was scary that way.
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