Deception as a hook? (spoilers)
I'm kind of tired of these movies that parse out the extremely relevant details to string the viewers along and then shuck all of the deliberate ambiguity for the last act of the film since it's information that vital to the plot. In this movie we're led to believe that Eric might be a good kid who was messed up by pharmaceuticals and a strict religious upbringing. We see him caressing his girlfriend by the lake with a ribbon and then we see his mom react severely to the discovery of that ribbon. Outside of a two second flash of a case file that Russel Crowe is looking at (which I only picked up by pausing my DVD player) there's no indication that he might be guilty of other crimes. Then he meets Lori and wrestles with homicidal urges throughout the duration of their trip. We're asking if he's truly reformed (as determined by the juvenile facility) or if Detective Crowe is right and it's inevitable that he'll fall into a murderous relapse.
Then we officially learn when Lori is in the squad car that all along Eric has been under suspicion of other murders and his parents were really murdered due to the discovery of the evidence (the ribbon). This is where I feel intentionally deceived as a viewer. We did have Lori's hints of having seen him kissing that girl by the lake (the aforementioned case file actually indicated he'd gone quite a bit further than first base) but I have a hard time believing the obsessed detective wouldn't have once mentioned earlier that he knows Eric is guilty of more murders than he'd been convicted for.
I also don't understand why Eric had been able to destroy all the evidence with the missing girls, but hadn't even attempted to disguise his guilt in the case of his parents. Also, how did Crowe know the motivation for their execution and why wasn't this evidence a part of his trial if he did know this? It just seems convenient for the narrative that there was a much greater indicator that Eric was indeed a psychopath, but those details were suppressed for almost an hour and a half to heighten the ambiguity.
I will say that this narrative technique did make the movie more compelling than it would have been if it had unfolded in a strictly chronological fashion, but the lack of organic development made it less satisfying. It just seemed like a buffer for the viewers' interest rather than allowing a reliance on the strength of the plot and characters. While it appeared we were supposed to question Eric's capacity to change, the ending told us that he was damned all along. He'd resisted the urge to murder Lori but Russell Crowe still managed to see to it that he didn't walk away from his unanswered offenses.
I do wonder if the book was structured the same way and omitted as many expendable details (like what the ribbon was or what happened to the Detective's wife).