In the months leading up to his death, U.S. Ambassador to Libya Chris Stevens worried about what he called the never-ending security threats in Benghazi and mentioned that his name was on an al Qaeda hit list, a source familiar with his thinking told CNN.

Stevens specifically mentioned a rise in Islamic extremism and al Qaeda’s growing presence in Libya, the source said.

Matthew Olsen, director of the U.S. National Counterterrorism Center, said Wednesday that it was unlikely that Stevens and his security team were killed by random protesters.