Help! Could a blocked soil vent/pipe ( from roof) cause sweet smell in bathroom - ? vandalism

[Bettyboo]

Bath, toilet and basin sink used regularly and water draining fine. All of a sudden have developed sweet strange smell in bathroom . I appreciate weather is hot at moment but it has never occured before .( I have had similar in another bathroom when traps have dried out so recocognise dry traps can be a cause)
I have a nasty jealous neighbour next door and last week he was up on his roof . He can easily step onto my roof and block the soil pipe from the top of the roof ( he has my lower kitchen drain before) Do you think this could trigger the smell please and would you know how best I can investigate myself initially ? can i put something down toilet/ basin/ bath? to see smoke/ stain? I cant tell where smell is coming from but I think may be from loo
Thanks for your help!

 

[Chuck]

Do the traps in the bath / sink gurgle when you flush the toilet?

Is the connect at the back of the toilet flexible, i.e. has a 'concertina' appearance or is it rigid pipe?

Some people describe the smell of a dead mouse as 'sweet / sickly'.

 

[Bettyboo]

Do the traps in the bath / sink gurgle when you flush the toilet?

Is the connect at the back of the toilet flexible, i.e. has a 'concertina' appearance or is it rigid pipe?

Some people describe the smell of a dead mouse as 'sweet / sickly'.

No the water in the traps does not appear to move much / gurgle , when I flush the toilet
the connect at the back of the toilet is not flexible its is rigid
can't see any mice around