I think he died of smoke inhalation as the autopsy revealed on purpose.
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What autopsy? Where was it done?
A Libyan doctor who treated Stevens said he died of severe asphyxiation, apparently from smoke. In a sign of the chaos of during the attack, Stevens was brought alone by Libyans to the Benghazi Medical Center with no other Americans, and no one at the facility knew who he was, the doctor, Ziad Abu Zeid, told The Associated Press. Stevens was practically dead when he arrived close to 1 a.m., but "we tried to revive him for an hour and a half but with no success," Abu Zeid said. The ambassador had bleeding in his stomach because of the asphyxiation but no other injuries, he said. Read more at http://www.snopes.com/politics/military/stevens.asp#tKPp3z9rUjl7Sxch.99
I got this from Snopes.
Not sure if there was yet another full autopsy done or not.
An autopsy would also show a sexual assault that occured pre or post mortem.
We’ll never be told what happened by this gang.