Just to offer a 'too' speculative theory (for fun): imagine those fertiliser bottles were Vasko's, Borce's, or a mate of theirs, and imagine Vasko/Borce/their mate disposed of them somewhere, woop woop.
Then, imagine the cops, knowing this, decided to pick up those bottles and keep them.
Then, imagine, Karen's body is found and the cops decide to put those bottles near Karen's body...
Why would the cops play this little ridiculous ruse of shifting the bottles to near Karen's body? It would put the cat amongst the pigeons, would it not?!?!?! Once the owner of the bottles (Vasko, Borce, or some pal of theirs) saw them, they'd think, oh no, what is going on here!! Then they'd want to phone someone to discuss the matter, would they not? But the cops are wiretapping phones, aren't they? That then poses the MOTHER of all dilemmas, does it not? If someone (Vasko) phones someone else (Borce), he'll have to have one of those now all-too-familiar 'code' telephone calls, right? The ones we read about gangsters having while ordering "pizzas", or talking about "dvds", or discussing "going fishing" or something like that. THAT would then provide the cops with invaluable info.
i.e.
Vasko: Guess what?
Borce: what?
Vasko: the apples are where the meat pie is.
Borce: WHAT?!?!?!
Vasko: can you believe it?!?!
Borce: How did they end up there??!?!!!!
Vasko: I wouldn't have a clue mate!!!
Borce: Did you move something?
Vasko: no way mate.
Borce: was it you?
etc.
That would provide valuable information to the cops as to who knew about "apples" and "meat pies" and locations...
OBVIOUSLY this is a tad far fetched- having the cops move the fertiliser bottles- but it is an interesting grand speculation LOL
thanks for reading haha!