Star Wars: The Clone Wars - Season 2 Episode 19 -

When the Zillo Beast is brought back to Coruscant in hopes of learning the secret of its impenetrable armour, it instead breaks loose and rampages across the ecumenopolis. As the clones prepare to kill it with poison gas, the Jedi are again trapped in a moral conflict between the value of its life and that of the planet's civilian populace.