To be fair, I think the "slim chance" of conviction means a slim chance of convicting on the highest possible charge, rather than a conviction at any level. For instance, there might be a slim chance to convict of first degree murder, but greater chance at second degree or manslaughter. In some cases an accused might be willing to plea bargain on the lesser (but still serious) charge, but fight all the way to avoid a longer prison sentence. I doubt if Alberta prosecutors are generally sending cases with a slim chance of conviction to trial.