The evidence was likely throw away because it was no longer in shape to be of any use. It had been allowed to deteriorate by being improperly stored. Given the shape it was in, there was little or no chance any DNA would ever be found on it. Also Lynne Harper's body was in such bad shape that finding any DNA was impossible.
This makes it impossible to prove whether Truscott raped and murdered her , although the Harper family to this day belive he is quilty and there is enough circumstantial evidence to uphold the conviction.
Truscott was given an acquittal because he had already served considerable time, the evidence had deteriorated and was now useless, nearly 60 years had passed, witnessess had died or their memories had faded and there was no chance the Crown could have gotten a conviction.
Although they acquitted Truscott, the Crown made a point of declaring that he had not proven his innocence.