Absolutely! He has committed a huge crime that will - please God - put him away for the rest of his life. But intellectually, he is no master criminal! His biggest downfall was the arrogance of believing he was cleverer than the police. This makes me think he must have previously got away with something major, and it gave him the feeling he was invincible.
This sounds plausible to me - as I mentioned on my earlier post, I believe he felt wrong-footed by the police: he was so detached with reality as to think that Helen would become 'just another missing person' in spite of the trail of suspicious pointers in his direction... and as most of the posters here concur, you don't suddenly become a monster in middle age, he must have done stuff before which made him cocky about his ability to get away with it - he sure lost his cool with the police: it was not part of his plan or what he anticipated...