I don't think they're intentionally throwing the case. I think some of the prosecution witnesses have been intentionally damaging the prosecution, but not unexpectedly. There's also the fact that some prosecution witnesses are local police who were maligned, often unfairly, by the national media, had the case taken away from them, and would be vindicated by an acquittal.
I think it's more that the prosecutors, by calling all every witness, even those that harm them, are falling back on the idea that prosecutors represent the people and are seeking justice rather than purely advocating for a conviction. That does give them an excuse to lose, which they should.
It's hard to reconcile all that with them seeking a conviction for second-degree murder, though.