A robber in a Halloween-style skelton mask threatened a shop security guard with an axe in Rossendale and made off with a cash box.
Detectives are appealing for information to catch the robber and his accomplice who sat in a getaway car outside the Co-operative Late Shop in Thorneylea, Whitworth.
The armed attacker struck as the 40-year-old guard was leaving the shop just before 8.30am on Saturday.
The pair fled in a red Peugeot 307, which was abandoned a short distance away.
The offenders ran down a footpath known as the old railway line which runs alongside the River Spodden.
They are believed to have smashed open the cash box with the axe, which triggered the release of a purple dye to stain the money as a security measure.
The two men then ran off, dumping the axe along the footpath.
Police tracked the thieves onto Dell Road, across Shawclough Road onto Paton Street, then to Foxglove Court and eventually Bassett Way, where the two offenders were last sighted. It is not known how much money was stolen.
A Lancashire Police spokesman said the security guard is a family man and has been left distressed by the attack.
Police are now examining the axe and the car.
DS Charlie Haynes said: “I am keen to speak with anyone who can provide us with any information about who these men are.
“We have recovered a number of items which we are forensically examining along with the abandoned vehicle, that we know was previously stolen from the Middleton area of Manchester.
“If anybody knows the identity of these men or any information regarding the robbery then I would urge them to contact police as a matter of urgency.
“Even the smallest amount of information could help as we search for the people responsible for this despicable attack.”
Both attackers are described as white men in their 20s, of medium to muscular build with shaven heads.
They were wearing blue hoody style tops or sweatshirts and tracksuit pants, however during their escape, they took off their pants and were then wearing grey shorts. Anybody with information should contact DS Haynes or DC Dodrill at Lancashire’s East CID on 01282 472518.