Genius London strikes again.

Because for one thing, sticks are biodegradable. Given time, they'd just dissipate into the forest floor. But, that would take time. The stick still has its advantage, though. Her fingerprints would be on the knife, yes, but no blood. The puncture wound wouldn't even resemble a knife's. And, say the police did figure out it was a stick. Have you looked around? They are in the middle of a forest. There are sticks EVERYWHERE. Just throw it deep enough into the woods or the corn field. Or, better yet, just burn it. All evidence is gone.

*rethinks life choices*