English word for "wada maaf gawah"

[Tom]

Hi

In my language, there is a beautiful court term "wada maaf gawah", which means:

wada = promise
maaf = forgive
gawah = witness of a crimnal (accomplice)

The accomplice who gives the police/ government/ or any other department information of the crime in which he himself was involved, but with the promise that he will not be trialed for that or forgiven for what happened.

The red part is very important.

So could you please tell me the English word for it?

Many thanks,

Tom

[Jamie (K)]

We say that the witness is granted immunity (from prosecution).