Why didn't Dumbledore think up a plan to use Veritaserum to prove Sirius's innocence? Like make him drink it and tell everyone that Wormtail escaped, or use it on Death Eaters in Azkaban to prove that Wormtail worked for Voldemort?
Also why didn't they use Veritaserum to prove that Lucius, Macnair, Avery, Nott, Crabbe, Goyle, Selwyn, Greyback, Yaxley and the Carrows willingly served Voldemort during the First Wizarding War??? That would definitely make them end up in Azkaban.
Could Dumbledore have used his wand to pull out the memory of Voldemort getting revived from Harry's head and prove to the entire world that Voldemort has returned?
Since Harry thought Severus was supporting Draco's evil plan in book 6, why not ask Severus to drink Veritaserum and tell his loyalty to Harry so that Harry won't suspect him?