Just to set the record straight, two were ex-SEALs, working on a project to recover lost Man Portable Air Defense Systems (MANPADS), the third was an Information Systems Officer with the State Department.
None of the three were on any Protection Detail for Ambassador Stevens, or any other State Department personnel. They were not Office of Diplomatic Security employees, and two were not State employees at all.
The two ex-SEALs heard the attack on the Consulate and immediately went to the Consulate, where they took weapons from the Libyan security guards and commenced a defense which allowed Consulate staff to escape to a supposedly safe location. They died in a defense at that location allowing staff to escape the attack there.