Early morning walkers might hold the key to a knifepoint robbery in Horsham Park.
The shocked victim remained aware enough to warn people not to approach his attacker.
And police are hoping that someone in the area might come forward to help their inquiries.
A suspect awaits further questioning on the reported incident after initially being interviewed by police.
Police have been told the 53-year-old victim was walking through the park about 8.45am when he was approached by a man who produced a knife and demanded money. The threatened man handed over some money and the robber then made him throw away his mobile phones and also put his watch on the ground.
Sussex Police has issue a public appeal for help in investigating the incident.
Detectives would like to speak to anyone who was in the area at the time of the robbery on Tuesday of last week and in particular anyone who spoke to the victim, who warned them not to go in the suspect’s direction as he left the park.
Sussex Police said in a statement : “A 21-year-old man from Horsham was arrested on suspicion of robbery and has been bailed until September 16.”
Although attacks in the park are relatively rare, there have been several serious incidents.
In January a foreign exchange student of 17 from Honk Kong was attacked and robbed by a gang of five people. Last August a young woman was raped in the park but managed to telephone for help.
Other incidents have included a racist attack on a 13-year-old British Asian and the jailing in 2012 of three men from Horsham for assault on a 29-year-old man who was stabbed with a bottle and kicked. That incident was seen live on CCTV by an operator.
Some areas of the park are covered by the public space CCTV network, there is a security contractor and also patrols by park rangers.