It sounded from the reports as if both of them were living on the edge of normal society - she was living in a hostel for homeless people in Salisbury - quite near to where they found the bottle - both were on drugs, and he constantly investigated rubbish bins skips etc for stuff he could use, eat or sell on. It was reported that both of them picked up discarded fag ends and smoked what was left in them. So a bottle of what looked like perfume in an original box, even if opened, would have perhaps seemed a good find.
We both grew up in Salisbury, and still visit quite often. In recent years, there have been a lot of changes - many homeless people begging on the streets, swathes of shops going out of business, and a very large proportion of the shops now turned into coffee houses and gift shops for the summer tourists, and of course, if they stop coming it has a knock-on effect. I'm not at all worried about going there - its one of those 'perception of risk' situations, isn't it, like when driving to the airport is hundreds of times more dangerous than actually taking your flight, but we all drive around all day just the same. And at least Salisbury Hospital has specialist skills at looking after patients with Novichok poisoning by now!