I still personally think the "partial alibi" was in relation to the sexual assault/rape charge and this is now why people are questioning Chanetelles relationship with the accused.
An alibi partial of not is only used to prove innocence. If he was claiming he had a sexual relationship with the accused to explain the suppressed charge, they would not be calling this an alibi, it would simply come out in court as a part of the defence case.
His alibi can only be used to prove he was somewhere else during the commision of the crime. See attached:
An alibi is a judicial mode of defense under which a defendant proves or attempts to prove that the person was in another place when the alleged act was committed; as, to set up an alibi; to prove an alibi. The Criminal Law Deskbook of Criminal Procedure [1] states: "Alibi is different from all of the other defenses; it is based upon the premise that the defendant is truly innocent." In the Latin language "alibi" means "somewhere else".
http://en.wikipedia.org/wiki/Alibi
Therefore the accused is claiming he did not commit the crime. If his DNA was found on the victim and he is going to claim they had a sexual relationship, this will come out in the trial to try and give the judge/jury "reasonable doubt" as to the DNA evidence. That is the point in a murder charge, the jury needs to find "beyond reasonable doubt" that the person committed the crime. We all know the OJ Simpson case and the majority of the world believes that he is guilty, but as soon his defence lawyers brought out the glove, asked OJ to put it on and then stated 'If the glove don't fit you must acquit', reasonable doubt was put into the minds of the jury. Whether they thought he didn't do it, or that there was some tampering of evidence, they had some doubts as to his guilt and so by law had to return a not guilty verdict.
The prosecution needs to prove you guilty, you do not need to prove your innocence (this is why it is said innocent until proven guilty). Maybe the prosecution case is not as solid as some might like to believe and that is the reason for such statements as below:
After the court appearance Detective Superintendent Grant Moyle said the investigation into the murders was still underway.
'I'd like to stress that it's still not too late to come forward with any information that anyone has in regards to the murder of Andrew, Rosemary and Chantelle Rowe,' he said.