A schoolgirl was left shaken when a man exposed himself to her.
The man got off a bus at the Dorsten Square stop in Crawley on Friday and exposed himself to the 12-year-old girl.
A woman intervened and took the girl away from the scene, before the man left on a bus at about 6.35pm.
A 62-year-old man from Crawley was later arrested on suspicion of engaging in sexual activity in front of a child. He was questioned before being released on bail until August 28.
Detective Constable Penny Furtado said: "This was a very upsetting experience for the schoolgirl and we are keen to speak to anyone who saw what happened.
"I am particularly keen to trace the woman who helped her get away from the man. If you know who the woman is or where she could be, please contact us."
Anyone with information should call 101 quoting serial 1362 of 11/7, email email@example.com or call the independent charity Crimestoppers anonymously on 0800 555111.