For matters this serious, you can't just act unilaterally and report afterwards.
Tips
history
Originally a privilege granted to trusted generals or magistrates: execute (斩) a criminal first, then submit a memorial (奏) to the emperor. Attested in the 《汉书》 (regarding Shentu Jia) and later dramas.
usage
Can be positive ('decisive action') or negative ('bypassing proper channels') depending on context.