Yes. From his
biography: "Mr. Zimmermann was counsel for a leader of the Branch Davidian religious group involved in the shootout with the Bureau of Alcohol, Tobacco and Firearms and the subsequent 51 day stand-off with the FBI near Waco, Texas. He spent two days inside Mt. Carmel Center before it was attacked with tanks and CS gas, with 76 people perishing in the fire that erupted. Mr. Zimmermann later testified before Congress in nationally televised hearings."
