DETECTIVES investigating an armed robbery at a post office believe the masked culprit may have targeted other businesses before his raid.

Wet weather may be partly to blame for the lack of witnesses to have come forward since the robbery in Darlington on Thursday.

The attacker entered the Harrowgate Hill Post Office, on North Road, at about 3pm, brandishing a weapon believed to be either a knife or a blunt instrument.

He threatened a member of staff and made off with what has been described as a "large amount" of cash.

Although he was wearing a bright yellow jacket, and was 6ft tall, it is thought he may have gone unnoticed by pedestrians keeping their heads down from the rain.

Police believe he made off on foot through streets near the post office and possibly through North Road Cemetery.

Detective Sergeant Ian McGarleysaid the man may even have been seen in the days and weeks leading up to the attack checking out other businesses in and around the town.

He said: "Quite often it's not the first place that they have looked at that they pick on. Have any people in other premises been suspicious of anybody hanging around their business?"

Anybody with information is urged to contact Darlington police on (01325) 467681.