A teenager was sexually assaulted after leaving a nighclub on the University of Essex campus.
The victim, who is 18, was attacked at about 0200 BST just off a path at the back of a lecture theatre.
She described her attacker to police as being in his 20s, dark skinned with short dark hair and about 5ft 8in (1.73m) tall. He was of medium to muscular build.
Anyone who was in the area at the time is asked to contact police.