Several Yemenis belonging to al Qaeda participated in the terrorist attack on the US diplomatic compound in Benghazi last September, sources told CNN. One senior US law enforcement official said "three or four members of al Qaeda in the Arabian Peninsula" took part in the deadly attack, CNN reported on Thursday evening. Western intelligence services said the men may have been sent to carry out the attack or may have already been in the city and took part as the opportunity arose, CNN reported. The attack on the compound and a safe house left four Americans dead, including US ambassador to Libya, Chris Stevens. One source said counterterrorism officials learned the identity of the men and established they had spent two nights in Benghazi after the attack. They were later traced to northern Mali, where they are believed to have connected with a group commanded by jihadist leader Moktar Belmoktar, a senior law enforcement source told CNN.