Depending on the edition, speak with dead requires the corpse to have a working jaw, so just destroy that. If you hide the head, someone can just find it.
This is all stuff you'd have a reason to know in character when a setting includes something as impactful as the ability to use the dead as a witness. If the victim can be a witness, you need to either fool or silence the victim post-mortem.
There are many ways to keep a witness from identifying you. You just need to be creative.
Yes DM, this comment right here.
Depending on the edition, speak with dead requires the corpse to have a working jaw, so just destroy that. If you hide the head, someone can just find it.
Can a dead body without a tongue still speak when affected by speak with the dead?
I believe the requirement is jaw not tongue.
This is all stuff you'd have a reason to know in character when a setting includes something as impactful as the ability to use the dead as a witness. If the victim can be a witness, you need to either fool or silence the victim post-mortem.