The Branch Davidian compound in Waco, Texas, is shown engulfed by flames in this April 19, 1993, file photo. Retreating from its past denials, the FBI is acknowledging that federal agents fired one or more incendiary tear gas canisters during the standoff with Branch Davidians, while maintaining its stance that it did not start the fire that consumed the compound with Koresh and more than 80 followers inside.