A gun smeared with traces of a suspected killer's DNA cannot be directly linked to the murder of a takeaway boss, jurors have heard.
Tipu Sultan, 32, was gunned down by a killer using a sawn-off shotgun at the Herbs & Spice Kitchen in South Shields as he cleaned up with his father last April.
Prosecutors claim Michael McDougall was the gunman, who was driven to the scene by Michael Mullen on a motorbike.
Both men deny murder, manslaughter and possession of a firearm .
McDougall, 47, of Hylton Avenue, South Shields, denies a further charge of firearm possession.
Mullen, 24, of Hawthorne Avenue, South Shields, denies an additional charge of perverting justice.
Both men are being tried by a jury at Newcastle Crown Court.
Jurors have heard a sawn-off shotgun, which had smears of blood containing traces of McDougall's DNA, was found by children playing in grassland last summer.
An expert has told the court how forensic testing cannot link that gun to the murder weapon used to kill Mr Sultan, from Sunderland.
Sharon Fowler, from the National Ballistics Intelligence Service, told jurors she examined wadding found on Mr Sultan's body which had been deposited by the gun that killed him.
She also examined wadding left from test fires of the gun found by the children.
Both sets of wadding contained unique marks, but they could not be matched to each other.
She told jurors: "I think, in my opinion, the crime scene wadding recovered from the fatal shooting was not fired from that gun."
The expert said outside factors such as where and how the gun had been stored, as well as how often it had been fired, could affect the outcome of such testing.
She said the weapon, which has been produced in court and shown to jurors, has not been linked to any unsolved crimes on the ballistic database.
The trial continues.