From: Rabbi Akiva Eiger
To: Unknown recipient
Rabbi Akiva Eiger addresses whether a relative or disqualified person accepted as a witness who is subsequently found to be an ed zomem is subject to Biblical hazamah penalties. He argues that such persons never acquire the inherent legal status of 'witness' (shem eidus), and therefore the Biblical penalties do not apply to them; he also revises an initial position regarding a valid single witness accepted as two, based on a Yerushalmi cited by the Ran, leaving several difficulties unresolved.
Source: Shu"t Rabbi Akiva Eiger §179