hostile witness

Translations
враждебный свидетель
The defense attorney declared the witness a hostile witness.
Адвокат защиты объявил свидетеля враждебным свидетелем.
Definitions
A hostile witness is a person who is called to testify in a legal proceeding but shows an unwillingness to cooperate with the party that called them, often providing testimony that is unfavorable or contrary to that party's interests.
Words
hostile

adjective
враждебный
witness

noun
свидетель