IMO, if they weren't lying in a prominent position such as the hall table, where the husband would have seen them the last time he was there, how would a home invader know about them, look for them, or find them?
I find it a strange comment by the husband. Was he suggesting his wife got out the handcuffs to play master/slave with someone, when he wasn't home?
I was wondering if the handcuffs were in Janet's jewellery box or in a drawer of her dressing table. The killer makes Janet put on jewellery so perhaps he spots the handcuffs?
It is a very strange comment though. Why didn't he ask about them when he first saw them years earlier?
The master/slave scenario is very interesting. Handcuffs weren't unusual amongst consenting couples, but the husband doesn't know why they might have been there.