The Tortured Ending

So yesterday i watched this film staring Jesse Metcalfe and Erika Christensen which was released in 2010, The Tortured.
So it wasn't the greatest film ive seen but the ending does seem to cause allot of confusion and speculation in fact the minute the movie ended i hit google! But i didn't really find many good answers, after a little thought i think i may have a good idea of what happened.

Ok a quick plot summery for anyone who has not seen the film.
Happily married couple have a six year old son called Benjamin who is kidnapped right from his front yard by a sadistic serial child murderer Kozlowski, of course the boy ends up being found dead in this killers basement.
At the trial it is revealed that there were various bodies/bones found buried in his back yard yet he is only sentenced to 25 years in prison. The mother who is obviously furious tells her husband she want him to help her kill this murder he says no, they split, skip ahead a couple months and the father comes around to the idea. They watch as the killer is being transfered outside the prison follow the van and manage to get laxatives into the guards coffees (medicine they acquired due to the husband being a doctor) they obviously stop the husband hops in the van, with the wife following in the car, the husband loses control and flips the van over a bridge he is surprisingly ok (yeah one of those films) but the prisoner was thrown out the back of the van and is unconscious. They end up in an old house in the middle of know where, which is where 'plan revenge' begins to take place. After some disturbing shit like soldering irons being held on his chest and stomach, being used as an ash tray, then being injected with something that causes all of his muscles to spasm at once (original) then one of the worst for me being injected into his ear drum with something awful. Then the image on the cover they use an old gas mask to temporarily suffocate him because that is how he killed their son, during this he goes too far and ends up having to be resuscitated. Throughout all of this being injected with something to keep him conscious the entire time.

OK here is where the problems start they pull out the breathing tube they had down his throat, which is when he tries to plea with them, telling them he had no idea who they where and even no idea who he was and that all he could remember was a car crash. Now conflicted on what they should do and how they should feel about torturing a man that had no clue what he had done, they decide it doesn't matter its still the same man. For some reason they are insanely driven to have the man say their sons name and to persuade him, they pop his foot in a vice and almost crush it as thin as a pop tart! Which has him scream out benjamin (though this really doesn't make sense because he heard them say the boys name earlier when he was suffocating him so he was going to know his name whether he knew the child or not) which they take as a sign that he remembers. Any way he escapes and for some random ass reason he goes upstairs?? Is obviously knocked out, but as being carried back to his basement of pain he wakes up freaking out the wife in turn making the husband fall down the basement stairs and letting the killer get away. while all this is happening the police and u.s marshals are homing in on the house, obviously looking for the escaped criminal. As the killer escapes the police are seen capturing a convict in an orange jump suit, which turns out to be Kozlowski the convicted child killer. Which is where the TWIST of the movie is kinda explained, what the couple had not seen was another prisoner being transported with the murder an average joe sorta fella who had been convicted for some fraud, and of course that was who they had been torturing, when the van crashed Kozlowski had escaped with just a gash in his leg. So back to the story, the couple are searching for the guy they had been torturing and they find him the moment he jumps of a chair in an abandoned shed with a rope around his neck, but the most confusing part for people is the fact he had a note in his hand (when did he have the time to write that?) which said he was sorry for what he had done and he was a bad person who may have deserved what they had done to him. WTF!? Right, so my conclusion is this poor fraudster who had lost his memory and all he knew was these people telling him he had murdered their child and punishing him for it had no choice but to believe them and the only thing he could do was apologize for it and kill himself. And as far as i could tell the couple never found out they had tortured the wrong man. So yeah pretty much a half assed explanation of the twist from the film makers but yeah that was my idea.