A footprint embedded into the bruised forehead of a robbery victim is the main piece of evidence that could lead investigators to his attacker.
Bar landlord Johnathan Robinson, 33, was hit by a car and knocked over Monday as he left his Salford, England, pub with about $3,522 in cash.
As he lay on the ground with a broken leg, one of the attackers walked up to him and stamped on his head before taking the money.
Officers are now checking shoe databases and speaking to manufacturers to find a match for the footwear.
"It is a vital clue," Detective Sgt. Julie Connor, said.
Police believe the gang may have come from the nearby Clifton estate. The Volkswagen Golf the thieves drove was stolen from the estate early Sunday and dumped near the bar.
It had false license plates that were stolen from another vehicle in Wigan, England.