What supports a circumstantial reading of “wa-huwa muṭmaʾinnun” after the researcher entered?

Supplementary Practice 10: Rhetoric of Claim, Evidence, Objection and Reply

• Muṭmaʾinn is always an absolute object
• Every wa-huwa clause expresses an oath
• It describes his condition at entry and the pronoun links to its owner
• The action of entering must be negated