Guilty or not? Who did the crime and did they do their time?

Chapter 15 Guilty, raised the question who killed who, on page 175 Brayford accused Corrigan of being the true murder of Shelley Napope, Brayford said "I put it to you that the girl (Shelley Napope) didn't get stabbed to death, she got strangled, and it was your hands that were around her neck. And the reason you were doing it was because she said she was going to charge you with rape. Isn't that correct?" and before that Brayford accused him of killing Janet Sylvestre because witnesses said that they saw him with her at the bar the night she died (Corrigan said he was and then he said he wasn't in Saskatoon the night she died).
Although when they took Crowford in and question Mason, Mason had a different story. " Mason admitted to have taken Janet Sylvestre to his house were John Crowford proceeded to rape and beat her unconscious, whereupon the two me took her from the house and driver out into the country. But then Mason changed his mind." pg. 138
On page 207 the last section the continues on to page 208 Crowford said that Corrigan was the one who killed Shelley not him, according to the text Corrigan took Shelley in the bush stabled her, the went to the car and told Crowford and then Crowford went and stabled Shelley several more times to make sure she was dead.
So basically, it were peoples words against each other and there was really no evidence beside verbal for these murders. Although when Crowford did take the stand to defend him self and proceeded to say he didn't do these thing after he had admitted it, and again later admitted it again it is hard not to think he is the one to blame for all the deaths including Janet's and Shelley's.
Although the question still stands that should Corrigan and Mason also be arrest for accessory, rape and maybe something more. I don't believe that these two men should have gotten away with what they did so easily and their involvement in what happened to these girls as well as others should have been push aside and ignored. This book did have justice but not all the justice that should have happen, happen and bad people got away. I am not sure who is to blame for Shelley's or Janet's deaths all I know is that one man go what he deserved even though some got away. Although there maybe more bodies and more villeins then we know but we don't know where they are and who committed the crime.
What do you think is any of this possible?