One of the suspects in last week’s attack that killed the U.S. ambassador to Libya and three other Americans is a likely al Qaeda member who was released from Guantanamo Bay in 2007, Fox News reported Wednesday.

Sufya Ben Qumu, a Libyan, was released into Libyan custody under the agreement that he would remain in custody, unnamed “intelligence sources” told Fox. He is believed to have participated in, or maybe even led, the attack that killed Ambassador Christopher Stevens and the three others.