WASHINGTON (AP) — Well-trained attackers executed the deadly dawn assault on a CIA complex in Benghazi, Libya, suggesting different perpetrators from those who penetrated the U.S. diplomatic mission the previous night, according to newly revealed testimony from top military commanders.

The initial attack, on Sept. 11, 2012, killed U.S. Ambassador Chris Stevens and communications specialist Sean Smith and set the mission ablaze. Nearly eight hours later at the CIA complex nearby, two more Americans, contract security officers Tyrone Woods and Glen Doherty, died in a mortar attack that showed clear military training, retired Gen. Carter Ham told Congress in closed-door testimony earlier this year.