He left blood splattered socks and the bloody glove on it, though... who knows what he might've done in a hurry? On the other hand... wouldn't the investigators have noticed freshly turned soil at the burial location?
The DNA will tell the story.
Why would there need to be “freshly turned soil” to bury a knife? It’s not like it’s a large object. It seems simple enough to just drive the blade straight into the ground, and then step on the hilt of the knife until it goes all the way in. If it was pushed in far enough with the heel of a shoe, nobody would notice it.