If it appears by affidavit that the testimony of a person is material in any criminal proceeding, and it reasonably appears that it will be impossible to secure his presence by a subpoena, a judge shall inquire into the conditions of his release pursuant to this article.
Code 1950, § 19.1-109.6; 1973, c. 485; 1975, c. 495; 1999, cc. 829, 846.