Police were called to Lower Street, Pulborough to reports of theft of a secure cash box around 11.50am on Wednesday, May 21.
A cash box was grabbed from a man working for G4S making a delivery to Barclays Bank but was found empty a short time later in a field near Rectory Lane.
Detective constable Laura Sinden said: “The suspect was seen leaving the scene heading towards the station and the A29 wearing a dark blue hoody with their hood up.
“We are not sure at this stage whether the suspect was a man or a woman as the victim did not get a clear view. We are appealing for witnesses to anyone who was in the area who might have seen anything suspicious is asked to call us on 101 quoting serial 561 of 21/5.”