One murderer, one sheath, an item that the witness mistook for a small vacuum.
Possibly a small bag or container of some sort.
I have always "pictured" BK parking on the street behind the house with a ton of plastic covering the inside and possibly the outside of his car. Then I picture black tie trash bags on the ground next to the car.
Then hiding behind the house as he travels down to the 2nd floor sliding glass door because he had checked in the past finding it to be an easy access point.
I see him putting every bit of clothing and weapons and every piece of plastic into the bags. I picture the car trunk covered with plastic and BK throwing everything into it.
Then he has a minimal amount of clothes stashed near by.
I believe he had a hole dug or a water plan to get rid of all this evidence. I also believe he got rid of his 2nd set of clothes maybe driving naked. Country roads helped him to have less coincidental interaction with police.
I believe he was obsessive washing his car inside and out and deliberately got rid of the shower curtain after going home to take a long shower.
I believe he was extra careful not to transfer blood evidence or to leave any internet digital evidence.
However, his plan did not go as planned. People were awake at 4:00am, dog noises, 2 people in MM's bed, witness seeing him walk by, footprint by DM's door, detectives watching him using his neighbor's trash, car caught speeding away from house in a hurry, suspicious sister, and worst of all - losing the sheath with DNA that matches his cheek DNA.
2 Cents.