Was Alex really a bad guy?

After Detective Loki takes Anna to hospital, there is a scene where he is sitting on the hospital bed reading the newspaper. The headline reads "Barry Milland aka Alex Jones reunited with family after 26 years".
Holly previously tells Keller that Alex isn't actually her nephew and that he was the first child she and her husband abducted.

This is one of the only issues I have with the movie. We know that Alex was kidnapped, drugged and obviously brain damaged to the point we see him in the movie. He's supposedly dumb enough that he can't understand what he's being asked, but he's also aware enough at the exact moments to taunt Keller and to sing the girls' song only when he thinks nobody is listening. So someone like him would have obviously been tripped up into revealing information either by the detective or while being tortured. I probably would have removed the part where he tells Keller that they didn't cry until he left them, then you can plausibly say he isn't answering the questions because he doesn't think he knows the answers.