in the last year. cnn s jim boulden has that. reporter: at daybreak, april 21st, 2010, it became clear just how deadly the explosion was on the deepwater horizon oil rig the night before. 11 workers killed, the well had broken. oil was spewing unabated into the gulf of mexico. weeks went by. the well could not be shut off. clean-up would cost billions. the gulf and bp were changed forever. i think it s very difficult to change a company like bp within 12 months. i think obviously it s the personnel who have changed. the attitude towards safety has definitely changed. the asset base has definitely changed. reporter: here s a breakdown of those three changes. bp and its then ceo tony hayward were under attack by fishermen,