plot holes (spoilers)

At the end, when packing up the boat, Andrzej would have noticed that the boy's rucksack and belongings were missing. I don't think Krystyna was in any sort of mood to help her husband cover up a murder, so why wouldn't he be suspicious of that, or even ask about it?
Also, the cabin would have smelled of sex, and Andrzej should have smelled it. You can't tell me he wouldn't recognize the scent of his own wife's snail trails. :-)