He prowls into bedrooms of Mother in Law's house

Your friend needs to tell her daughter, as unemotionally as possible, that she does not want her son in law to go into other rooms in her house without invitation, and leave her to deal with it as she will.
When the son in law visits again she needs to watch him like a hawk, follow him if he leaves the room, and again, unemotionally as possible, ask him directly if he is looking for something.
She also needs to check her possessions.
My uncle, many years ago, used to stay with my grandmother for brief visits and never went home without something: towels, travel blanket, old family papers, and his excuse was, when confronted, well, she never uses them, and I am her son. After he died and we had to clear his house, we were shocked at the amount of things he had accumulated, much of it actually belonging to my father. As a bank manager, one would have expected him to be a model of honesty.

It's unacceptable in my opinion. I wouldn't be able to resist saying something to him about it.

Mousetraps in the drawers.

Totally agree with your comments Apricity. Good post.

Various motives for the son in law prowling around his mil's bedroom have included bizarre sexual fantasies, checking out inheritance possibilities and being on the autism spectrum and not understanding boundaries. Standing at the top of the stairs and staring down at his mil when he was 'sprung' sounds more like very nasty bullying behaviour. And as we know all too well being intelligent in a well paid position does not mean someone is not a nasty bully. Quite the opposite.

Whatever the reason for son in law's prowling the fundamental issue is that it is rude, intrusive and totally unacceptable behaviour as a guest. You do not enter private rooms (which includes bedrooms and studies) in someone else's house without the person's knowledge and permission. You do not need to put locks on doors in your own house but you may need to manage your guests behaviour.

The fact that this needs to be spelt out to the son in law and everyone is worried about upsetting the daughter suggests that there is something very odd about the sil and the relationship between the daughter and her mother. The sil needs to be told very clearly that it is not acceptable behaviour and if it happens again he will not be welcome to visit. Bullies need to be called out.

Interesting that you mention autistic spectrum as I have a cousin who I suspect to have ASD who does this. Once I went to put something into the oven and came back to find her rooting in my cupboards and drawers.

People with ASD often don't understand normal boundaries - so if, for example, he was interested in looking around the house it might not occur that this is not socially acceptable. My dd and her bf (both diagnosed with Aspergers) don't get social norms either - they'll both wander into my bedroom for a chat even if I'm in bed in my nightie!

I still don't understand why he wasn't asked what he was doing the first time he was caught out. Just a spontaneous reaction to seeing this odd behaviour.

Sorry to ask this but is there any possibility of sexual fantasies going on in his mind? We came across a similar situation with a teenager female who had fantasies about her Uncle. In the end we caught her going through his clothing on a family visit and she admitted her fantasties were of a sexual nature.

I too wondered about aspergers or similar and maybe there’s a few clues in one of your posts you talk of his pristine and neat home (might be a bit of OCD there) then you mention his ‘geeky’ friends again a bit of a clue??? Of course none of this excuses his behaviour but maybe his guidelines are different to others
I still find it remarkable that nothing was said I can’t imagine looking up and seeing him up my stairs and not either saying ‘ what are you wanting up there’ or at least a bit more humorous with a ‘ have you got yourself lost’ or something similar I cannot see why your friend doesn’t speak to her daughter about it not in an accusation way but just a questioning way
It all sounds really bizarre

Tilly Could he be checking to see if your friends partner is maybe not looking to become a more permanent fixture in her life and could upset any inheritance he may have his eye on.
If he has done this before and comes across a locked door this time he goes snooping surely he would realise he has been rumbled if he is so clever,I wouldn't put up with it and tell him straight he needs to use downstairs facilities from now on.

I don’t know ladies, my childhood best friend is on the spectrum and I have never in thirty years had to specifically tell him not to go through my stuff or inspect my house when my back was turned.

I think a bloody locked door is something most folk I know on the spectrum means ‘no entry without permission’.

It’s difficult not to impute bad motive to SIL here on the facts as presented. At best, this behaviour is extremely weird.

I am of the "speak first and think later " nature ! I would not think twice about asking him what he was looking for , surely her DD is aware of what he is doing , no one prowls round my house and even when SIL comes in to do some task for me , he hovers in the doorway and won't come in till invited

I find it hard to understand how she's afraid to say anything.

There doesn't have to be a row - she could just quietly tell him that anywhere (presumably) but the loo/bathroom is off limits, and will he please not go into other rooms again. And refuse to discuss any further.
The SiL is the one who's being U - not your friend.

No, it wouldn't be very easy or pleasant, but it def. needs to be said.
(My inner nasty cynic can't help wondering whether he's looking for her will!)

People on the autistic spectrum don't recognise hints. They like things to be cut and dried with no nuances.

Why didn't he take the 'hint' when she put a padlock on her study door?

If he is on the autism spectrum he'd probably appreciate being told in a straightforward way that it's not on to wander about in someone else's house. Take the emotion out of it and just offer the facts.

I agree I would be there with my hands on hips
And a "Yes. Can I help you?"

However I do understand that with him standing at the top of the stairs looming over her together with the fact that he is quite tall could make your friend feel at a disadvantage.

If she was to wait until he was seated (no longer having the height advantage) stand in front of him (the School Mistress approach).
And politly ask if he was looking for something in particular?

Other than a lock on the door (sad in your own home) I would suggest keeping personal papers, money and jewellery etc in a lockable filing cabinet.

Tillybelle Is your friends Sil completely unaware how heavy footed he is?

Katek Crikey! I would have made sure he knew he had been struck out of the will!!
My reactions are very like muffinthemoo but then it didn't happen to me in my house. My feelings of outrage are for my friend and I feel it is completely unacceptable behaviour with no excuse, something one learns from about the age of 5, but then if it happened to me, I might feel frightened in truth. This man is very tall for a start.
I am sure all these replies will help my friend.
Incidentally, she did ask me could he have Autistic aspects or be on the spectrum. I've met him long ago and never picked this up. I did research in it so am pretty clued up. I still say, even with Autism spectrum disorder, it's inexcusable! My feeling, I am very sorry to say, is that he is judgemental about her life, which is busy. She is involved in a lot of charity work and works selflessly for others, so has a lot of things pertaining to this and is always busy. He has a meticulously and pristinely tidy and neat home where it is hard to imagine anyone making a cake and spreading flour around. He is always making his house bigger and better. My friend's house is truly a comfortable home. I think he is snooping so as to gossip about her house and criticise it, perhaps with his wife but more likely with his geeky friends. It's the only thing that fits my knowledge of him.

BlueBelle Actually it was my friend who is going through this and who phoned me for help. She was in shock, even hours afterwards. I said shall I ask Gransnet as she doesn't use any social media. I can both imagine both saying "What did you want upstairs?" and being struck dumb by the unbelievable rudeness of it. Indeed I have had some things happen when I should have made a very pertinent reply or asked the right question but all I did was just stare in disbelief and shock. I do identify with her feelings and about trying to deal with it. She does not want her daughter put in the middle between her mother and husband and is troubled in case her daughter is coping with other strange revelations of his behaviour but keeping going bravely. Very difficult for her.

MawBroon " *you have to be able to trust your family*"
Well said! That is the crux of it! I thought by writing to you all I would get a common-sense range of views I could help my friend appreciate. I am hoping she is reading this. I think she is in shock and perhaps scared of a row or bad feeling. I cannot be sure. To have to lock up your upstairs rooms is really extreme, I think. It is still bothering me a lot. Do you think our children's generation (40+ somethings) think they run our lives and can do what they like? It is so disrespectful! But trust is the most essential thing, you are completely right.

Very difficult. I can quite understand why she didn't say anything. I think I might be the same, just wouldn't want to rock the boat so wouldn't say anything. If it happens again I think I would have to say, can I help you or get you something. It really is an unpleasant situation and depends what the relationship with the daughter is. If good, perhaps she could tactfully ask if she knew any reason for it.

It might not be anything sinister but certainly not normal behaviour I don’t understand why Tilly just looked at him and said nothing I d have said ‘what do you want upstairs can I get you something’ and why are you expecting your daughter to speak to him I do not get that at all, you saw him, you ask him
Strange all round

Absolutely outrageous behaviour.

Can she tell daughter that there can be no more visits at her house unless the prowling issue is addressed?

Completely unacceptable.

Sounds like he’s eyeing up the inheritance so to speak. I have a sil who actually started clearing fil’s bookcase and throwing things away when he was on holiday. It didn’t end very well, fil was very upset and angry as you’d expect.

Danni from TIlly's reply to me I think there's a bit more to the story...

But I'd do the same as you, I'd be standing at the bottom of the stairs with my hands on my hips saying "What the heck are you doing up there?!" (not to make light of the situation).