Dog walkers found the bag six weeks before Michael Sellers killed Gracie Spinks.
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Det Con Denise Sandall, who investigated the murder, told jurors the bag contained a Marks & Spencer receipt belonging to Sellers' father, who he lived with.
Narita Bahra KC, the barrister representing Ms Spinks's family, asked her about this receipt.
"It's dated 29 April 2021 and timed at 16:16 hours," said Ms Bahra.
"You know that as officers, if you want to, you can go back to a location and ask a store for their CCTV of who was using the tills at that time?" she asked.
"Yes, CCTV generally lasts 28 or 30 days so we would have been in time for CCTV before it got overwritten," said Det Con Sandall.
"So if somebody went on 6 May, they could have potentially got it?" asked Ms Bahra.
"Potentially, yes," said Det Con Sandall.
Ms Bahra asked Det Con Sandall about the debit card details on the receipt.
Det Con Sandall said it only showed the last four numbers of the card and the authorisation code.
She said these details could have been used to identify the card holder, but this would have needed authorisation from a judge - either by going to court or sending forms via email.