assurance, defense, exculpation, reply, retort, explanation, assertion, declaration, vindication, excuse, avowal, out, statement, allegation, profession, account, self-justification, apology, case.
Or he may have decided to arrange a convincing alibi,
and creep away, leaving the discovery to another.
And two out of three you mention were inside The Manor when the second shot was fired, so can prove an alibi.
Maybe you want to frame up an alibi