A “bin surfer” may have found a fake perfume bottle containing a deadly nerve agent just minutes after it was discarded by agents trying to assassinate former Russian spy Sergei Skripal, a police counter-terrorism chief has said.

A CCTV still, revealed for the first time at the Wiltshire poisonings inquiry, shows Charlie Rowley apparently on the hunt for valuables in charity shop bins in Salisbury city centre shortly after the Russian suspects were in the area.

Commander Dominic Murphy, Britain’s most senior counter-terrorism officer, told the inquiry he believes Rowley found the bottle and had it for more than three months – even moving home with it – before he gave it to his partner, Dawn Sturgess, who died after spraying the novichok on herself.

One of the central puzzles of the Skripal and Sturgess case is how a container apparently used to daub novichok on Skripal’s front door handle in Salisbury on 4 March 2018 came to be opened by Sturgess in Amesbury, eight miles away, on 30 June 2018.

The inquiry has heard that British police believe the Russian suspects, Alexander Petrov and Ruslan Boshirov, sabotaged Skripal’s door handle between noon and 12.15pm on Sunday 4 March. The pair are then believed to have walked towards the city centre and vanished from the sight of CCTV cameras for 33 minutes between 12.31pm and 1.04pm.

On Monday the inquiry was shown a still from a CCTV camera showing Rowley in the Brown Street car park in the city centre carrying a bin liner at about 4pm. Murphy said he believed the image showed Rowley “bin dipping”.

Rowley, who had drug and alcohol issues and was also poisoned with novichok, has said his memory is hazy but he believes he may have found the bottle in bins in the car park. He has told police, however, it was in late June, shortly before Sturgess was poisoned.

In a statement read to the inquiry, Murphy said: “I believe it is most likely that Charlie Rowley found the perfume bottle containing the novichok on Sunday 4 March 2018, it having been placed in a bin somewhere in Salisbury by Petrov and Boshirov during one of the periods when they were not captured on CCTV.”

Murphy confirmed that Rowley relocated from Salisbury to Amesbury on 18 May, meaning if the officer’s conclusion is correct, Rowley took the fake perfume bottle with him in the move. Murphy said the charity bins were emptied frequently, which meant the bottle could not still have been there in late June if it was discarded in March.

He accepted police may never be able to pin down for certain the movements of the bottle and a theory that the agents “cached” the bottle to be picked up later could not be disproved. The inquiry has also heard there remains a possibility there could be two bottles.

Attempting to recall when he found the bottle, Rowley told police: “I got a vague memory that it was just a quick look in, [a] rummage. I think the reason I remember is because the package was at the bottom and again I had to hop up, lean in, legs in the air, got it, looked at it, women’s, well Dawn will like that.”

The inquiry continues.