
takes a bullet to the face
from a person or persons UNKNOWN.
Breaking Bad Season 4, Episode 7

Unknown caller.
It's got to be them.
The Big Bang Theory Season 12, Episode 23

whose UNKNOWN provenance
jeopardizes
The Big Bang Theory Season 5, Episode 2

somewhere UNKNOWN.
And most likely...
Money Heist Season 3, Episode 2

Their identity is yet UNKNOWN.
Money Heist Season 1, Episode 12