It seems he was a good man who was pushed to the limit after his best friend and girlfriend were killed by Eli. He then knows that she is not human and tries to end it when he goes into her house. When Oskar startles him, instead of going after Oskar, he throws the knife away before Eli wakes up and kills him.
So was Lacke a bad guy?
No, Lacke was not a bad man.
Having said that, I have to say that he was no role model either.
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http://www.youtube.com/watch?v=0e3tGxnFKfE
http://tinyurl.com/LTROI-story
Depends on who you're rooting for.
Which likely depends on what you think about Eli and Oskar's relationship.
Which probably depends on your assessment of Eli's motivations.
No, he wasn't a bad guy.
shareIn any other film you'd consider him one of the good guys (trying to kill the monstrous vampire).
So, like others have said, depends on your point of view and who you're rooting for.