A 20-year-old woman was raped at the University of Sussex's Falmer campus.
The victim met the attacker while she was with a group of friends drinking outside their halls of residence in the early hours.
When she went to go to bed the man followed her into her room and forced himself on her.
Officers have spent the last week speaking to students and searching for the offender.
The attacker was black or of mixed race, 19 or 20 and between 5' 9" and 5' 11". He had Afro-style hair, a moustache and long fingernails, was wearing dark clothing and spoke in broken English with an accent.
Detective Sergeant Simon Dunn said: "The victim is understandably very shaken by what has happened.
"We urgently need to trace the man involved and to speak to anyone who was on the Falmer campus late on Friday night or early on Saturday morning.
"If you know the man involved or recognise the description of him, please contact us."
The victim reported the attack to medical staff at the university who contacted police on 24 September.
Anyone with information about the September 20 attack should email 101@sussex.pnn.police.uk quoting serial 993 of 24/09, call 101 or contact the independent charity Crimestoppers anonymously on 0800 555111.T
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