They claim the plan was to exchange Ambassador Stevens for high-level al-Qaeda prisoners.

I BELIEVE THEY WERE AFTER THE RELEASE OF SHEIKH OMAR.

Ask yourself these questions:

Why is it back in the days leading up to 9/11/12 - and the attacks on the Embassies in Cairo and Benghazi - Morsi and the Muslim Brotherhood were agitating for the release of Sheikh Omar.

And why is it that, at first, the USA Today wrote that the Embassy Attacks were about the release of Sheikh Omar?

And why, since Benghazi has blown up in Obama's face, has Morsi completely stopped agitating for the release of Skeikh Omar?

From the Washington Times:

An al Qaeda terrorist stated in a recent online posting that U.S. Ambassador to Libya J. Christopher Stevens was killed by lethal injection after plans to kidnap him during the Sept. 11 attacks in Benghazi went bad. 
The veracity of the claim by Abdallah Dhu-al-Bajadin, who was identified by U.S. officials as a weapons expert for al Qaeda, could not be determined. However, U.S. officials have not dismissed the terrorist’s assertion. 
An FBI spokeswoman indicated that the bureau is aware of the claim but declined to comment because of the FBI’s ongoing investigation into the Benghazi attacks. [...] 
According to a March 14 posting on an al Qaeda-linked website, Dhu-al-Bajadin stated that Stevens was given a lethal injection that was overlooked during the autopsy. 
The “plan was based on abduction and exchange of high-level prisoners,” the terrorist wrote on the prominent jihadist Web forum Ansar al-Mujahideen Network. “However, the operation took another turn, for a reason God only knows, when one of the members of the jihadist cell improvised and followed Plan B.” 
Dhu-al-Bajadin’s claim of assassination also was copied to the Ansar al-Mujahidin website from the al Qaeda-accredited website Shumukh al-Islam. That site is open only to members, and the claim initially was posted for Dhu-al-Bajadin by a member identified as Adnan Shukri. 
The reference to Shumukh al-Islam has boosted the credibility of the claim among some U.S. intelligence analysts. A Western intelligence official said Dhu-al-Bajadin is a well-known jihadist and a key figure behind a magazine called Al Qaeda Airlines.