The couple left critically ill after exposure to the Russian nerve agent Novichok were likely poisoned by something missed during the UK run decontamination operation.
Newshub Europe correspondant Lloyd Burr told The AM Show police in Amesbury are still trying to work out how Charlie Rowley, 45, and Dawn Sturgess, 44, were exposed to the nerve agent.
"These two people, these two local Salisbury and Amesbury people, they picked this up from somewhere and it was somewhere that wasn't decontaminated during March by this multi-million pound decontamination process," he said.
The March decontamination operation had taken over large swathes of Salisbury and gone as far as ripping up the grass in some areas.
Burr said the couple were known in the area as recreational drug users and lived in a social housing unit nearby. Ms Sturgess had spent time in the local homeless shelter.
According to friends of the couple before falling ill the pair had gone to Queen Elizabeth Park near their house for a picnic and disappeared into some bushes for around five minutes.
It's believed this may have been where they were exposed, possibly by finding a container or something containing the agent.
Burr says he's put his own safety "on the back burner" to cover the operation as he's so close to the decontamination.
Locals and people in the area have been warned to not touch any foreign items such as bottles, litter or packets on the ground.
Children and parents have been told to be extremely careful in parks, although Mr Burr admitted there aren't many parks available to be used at the moment as most are cordoned off to be searched and decontaminated.
Watch the full interview above.
The AM Show with Duncan Garner, Amanda Gillies and Mark Richardson, weekdays 6-9am on RadioLIVE and streaming live to the rova app on Android and iPhone.