A Tesco security guard chased a thief who had stolen two mobile phones from the store in Morton Lane, Beverley.
The crook got away but in the process he dumped a plastic bag containing his stolen goods, as well as his hat and coat.
The crime was reported at 7.40pm on Monday.
Police say the thief was seen entering the store carrying a white plastic bag into which he put two mobile phones, still in their boxes.
A security guard began following the man through the aisles and the suspect then ran out of the shop.
He crossed New Walkergate and headed along Dyer Lane and into Saturday Market, with the guard following.
The thief then turned off Toll Gavel and into Landress Lane and the security guard lost him.
But on the way back to the store the guard noticed the white bag, still with the phones in it, and the man's hat and coat in a skip in Saturday Market.
Police are checking CCTV from the area in an effort to identify the man.
He was aged 32 to 38 and about 5ft 8in. He wore blue jeans but, because he wore a hat, there is no more detailed description.
Any witnesses should call police on the non-emergency number, 101.
