Police are appealing for witnesses and information after a robbery in Horsham town centre.
It happened at about 5.30pm on Friday.
Three young men wearing balaclavas in West Street approached a 15-year-old boy sat with a friend outside The Lynd Cross public house and the Wilkinson’s store.
The boy was taken around the corner towards The Gym, and his bag was taken.
One of the three suspects was seen carrying a knife.
Members of the public saw what happened and intervened, challenging this suspect and helping to detain him in a nearby Waitrose store after a short pursuit.
The suspect was then arrested by police.
Officers have appealed for anyone who witnessed what happened, or who may have seen the three suspects together in the town centre to come forward.