BENGHAZI, Libya (AP) – Heavily armed militants used a protest of an anti-Islam film as a cover and may have had help from inside Libyan security in their deadly attack on the U.S. Consulate, a senior Libyan official said Thursday.

As Libya announced the first four arrests, the clearest picture yet emerged of a two-pronged assault with militants screaming “God is great!” as they scaled the consulate’s outer walls and descended on the compound’s main building.

The rampage killed the U.S. ambassador and three other Americans.