A medical expert told jurors that a student's cause of death could not be determined after her body had been in water for almost two months.
Dr Matthew Lyall said Libby Squire's body was recovered from the Humber Estuary seven weeks after she disappeared in Hull on 31 January 2019.
Sheffield Crown Court heard it was inconclusive whether she "was alive or not before entering the water".
Pawel Relowicz, 26, denies raping and murdering Ms Squire.
The Home Office pathologist told jurors the 21-year-old philosophy student's body was decomposed but two lacerations inside her top lip showed blunt trauma.
He said small haemorrhages around her mouth could represent "squeezing or compression of the neck or covering of the mouth".
However, the lacerations "could be caused in water or in life near the time of death", the court was told.
CCTV of final movements
Jurors were shown CCTV of Mr Relowicz and Ms Squire's movements from when she was last seen on Beverley Road on 31 January 2019.
Dr Lyall said the level of decomposition made the examination too difficult and the cause of death could not be established.
"There could have been injuries - we just can't see them," he added.
Jurors heard Ms Squire, who disappeared after she was refused entry from a nightclub because she was too drunk, would have been about two-and-a-half times the legal drink-drive limit when she died.
Toxicology tests showed she had 198mg of alcohol in 100ml of blood. The legal driving limit is 80mg.
Sperm cells matching the defendant's DNA profile were found in swabs taken from inside her body, Dr Lyall said.
He added hypothermia, drowning or asphyxia were all possible causes of death but the actual cause remained "unascertained".
Earlier on Thursday, the jury heard evidence from witness Sam Alford who heard screams of "desperation" coming from Oak Road playing fields, where the prosecution claim Mr Relowicz had taken the student before raping and killing her and then dumping her body in the River Hull.
Mr Alford, who lives near the playing fields, told the court he believed the screaming lasted between four and seven minutes.
Previously, the court heard Mr Relowicz was "prowling around the student area of Hull" in his car in search of a victim before he intercepted the "extremely vulnerable" Ms Squire.
But on Wednesday, the jury heard the married-father-of-two had told friends she "tried it on" with him on the night of the student's disappearance, before telling her to get out of his car.
The trial continues.