Detective Superintendent Martin Smalley of Humberside Police said: "While we have considered throughout the missing person inquiry that Libby may have come to some harm, Libby's death and the recovery of her body now leads us to solely investigate as a potential homicide.
"The post-mortem examination concluded late last night and at this stage, we will not be releasing any results for investigative and operational reasons.
"We have to protect the integrity of the investigation, which is live and very much active and ongoing, with one man who remains under investigation."
He added: "Libby captured the hearts of not just the people in Hull, but across the country, and as I have said before, the support shown has been overwhelming and my sincerest thanks to absolutely everyone who has been involved."
Mr Smalley said: "Our thoughts remain today with Libby's family and friends at this incredibly sad and devastating time for them.
"The loss of a loved one is always an upsetting and traumatic experience to go through, but the circumstances surrounding Libby's death will only intensify the heartache for her family.
"Specially trained officers continue in supporting Libby's family and we will do all we can to provide further support and assistance to them in any way we are able to.
"The University of Hull have also created a space for tributes to Libby, which is open to both students and the community to attend and remember Libby and offer any messages of condolence."