After the final meeting and Light's death, everyone in the room knew the truth. They knew that the 13 day rule was fake, and the rule about destroying the Death Note was fake, too.
They also had many evidences against Misa (the tapes, fingerprints, hair, etc.), and Light also screamed "Misa write their names".
At this point, they had enough proof that Misa was Second Kira, but why didn't they capture her? Why did they let her go?