Witness
noun
An evidence person is a witness, because witnesses are people who provide evidence (you know, with their mouths or something).
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
証人になる
to become a witness
証人にする
to make into a witness
証人に立つ
to stand as witness, to bear testimony
エホバの証人
Jehovah's Witnesses
他の証人
another witness
成人の証人
an adult witness
証人の出頭
the appearance of a witness
証人の証言
a witness's testimony
証人の場合
in the case of a witness
証人はいません。
There are no witnesses.
私も証人の一人です。
I am also one of the witnesses.
彼はエホバの証人です。
He is a Jehovah's Witness.