I will say that the group theory that Hakan is like Oscar is incorrect.
The book pretty much makes Hakan out to be a pedophile that Eli uses for her own needs. The film tries to imply that Hakan has not been around Eli for awhile on account of his murdering skills (or total lack thereof). Hakan is not supposed to be long-time acquaintance.
spoiler (click to show/hide)
The director has gone on record as saying he felt that Oscar and Eli have a happy ending, and if he had to guess, that Eli would make him a vampire.