Libby Squire’s parents still do not know how their daughter died.

Pawel Relowicz is the only person who knows how Ms Squire ended up in the River Hull, whether she was alive when she was put in the water or how she was killed on Hull’s cold, dark Oak Road playing fields.

Despite all the evidence gathered by Humberside Police about Relowicz’s sexual motive, previous offences, interactions with Miss Squire and their sexual intercourse, detectives had to contend with a major problem for a murder investigation – no cause of death.

Home office pathologist Matt Lyall, who conducted the post-mortem examination, was unable to determine the cause of Ms Squire’s death because her body had been in the water for so long when it was found in the Humber Estuary.

Oliver Saxby QC, defending Relowicz, told the jury: “They cannot say how Libby Squire died. They can’t even say she was killed.

“Dr Lyall’s clear evidence cannot even say she was killed.

“However much you are reassured that the prosecution don’t have to prove this or that, not being able to prove how the victim died, not being able to prove she was killed, these are two fairly big caveats in a murder case.

“It means one of the crucial aspects of the case, whether she was killed, perhaps the most crucial aspect of the case, the prosecution are forced to rely on inference, on carefully constructed arguments, on theories, in reality, to persuade you of what happened.”

But prosecutors told the jury that they did not need to establish how she died.

Their case against Relowicz was presented on the basis that the father-of-two must have killed Ms Squire due to the overwhelming circumstantial evidence against him and the lack of credible alternative explanations.

Richard Wright QC, leading the prosecution team, told Sheffield Crown Court: “It is not possible for the pathologist to determine how Libby died, but it is not necessary for the prosecution to demonstrate any particular mechanism of death in this, or indeed in any other case of murder.

“We say that you can be sure that Pawel Relowicz subjected Libby to unlawful violence at the Oak Road playing fields and that violence caused her death.

“Whether that be by asphyxiation, or by any other means, such as deliberately throwing her into the freezing River Hull in the sure knowledge that she would drown.”

During the trial, a juror asked the judge to clarify: “Does circumstantial evidence stack up in court?”

Mr Wright told the jury that it definitely did.

And he said that the crucial circumstances which should convince them that Relowicz was the killer included the fact that he was prowling the streets looking for “easy sex”, that he was a serial sex offender, that he had picked up Ms Squire in a drunken and confused state and that he admitted the he had sexual intercourse with her before she vanished.

Mr Wright told the jury there was no other credible explanation of how she got into the water.

The prosecutor ruled out suicide. He said that, despite Ms Squire having mental health problems, she was in the “best place in her life” and had showed no recent signs of being suicidal.

He also discounted her accidentally falling into the water, pointing out that she was terrified of water and scared of walking in dark places by herself.

And Mr Wright dismissed any suggestion that she was attacked by someone other than Relowicz, saying it would have been an “unholy coincidence”.