Eastern Libya’s deputy interior minister, Wanis el-Sharef, said Thursday a mob first stormed the consulate Tuesday night and then, hours later, raided a safe house in the compound just as U.S. and Libyan security arrived to evacuate the staff. That suggested, el-Sharef said, that infiltrators within the security forces may have tipped off the militants to the safe house’s location. The attacks were suspected to have been timed to coincide with the 11th anniversary of the Sept. 11, 2001, terrorist strike in the United States, el-Sharef added, with the militants using the film protest by Libyan civilians to mask their action. Libya: 4 arrested over coordinated attack against U.S.Inside ruined U.S. Consulate in Libya Killed in the attack were U.S. Ambassador Chris Stevens, information management officer Sean Smith, and private security guards Glen Doherty and Tyrone S. Woods. El-Sharef said four people were arrested at their homes Thursday, but he refused to give any further details. He said it was too early to say if the suspects belonged to a particular group or what their motive was. Libya’s new prime minister, Mustafa Abu-Shakour, said authorities were looking for more suspects. The FBI is also in Libya investigating the attack. A government official speaking on the condition of anonymity told CBS News the FBI is planning to send investigators to Germany to interview Libyan U.S. Consulate personnel who were evacuated there. 4th American killed in Libya attack ID’dAl Qaeda offshoot a prime suspect in Libya attackAngry Egypt protests reveal anti-U.S. tensions CBS News correspondent David Martin reports officials already have a prime suspect in the assault — a radical Islamic group called Ansar al Sharia. The name means “Supporters of Islamic law,” and U.S. officials describe it as an offshoot of al Qaeda. Ansar al Sharia is one of multiple Libyan militias operating in the city. At a news conference Thursday night, Hani al-Mansouri, the spokesperson for Ansar al-Sharia, denied that the group or any of its men took part in the attack. He claimed angry protesters simply stormed the consulate after security guards barricaded inside opened fire to disperse the crowd.