Disposable/stolen mobile phones.
You always leave a trail with phones.
Buy it - store video, plus cell tower tracking, plus destroy and dispose the phone with no possible link back to you.
Steal the phone - can video place you at or near the crime scene - cell towers instantly identify stolen phones - destroy and dispose of phone.
Purchase a stolen phone - sold to you by a criminal who has seen your face and has your DNA sample on the cash - cell tower - destroy and dispose.
My theory - almost no one who has the skills and the diligence to commit an untraceable crime is going to waste his talents and energy on a death threat.