I think there is a good few options of Elaina's attacker; Katherine (obviously), Damon, Alaric (the new teacher I think he might be a vamp.) or Tyler they did a close up on a shot with him an the moon. If you go by what happens in the books they could each be a threat.
Alaric seems difficult to read he has a old looking "ring." He told Jenna about him coming to Fells Church for a new start and that his wife was killed. I think he could have had a run in with Vamps. either they killed his wife an made him a vamp. or he killed his wife because he is a vamp. If you go by the Alaric character in the book he is a college student with an interest for vamps. he is also dating Elaina's best friend Meredith but she isn't in the show!
Just wanted to put this out there to see what everyone else is speculating
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