The State Department released this statement on October 11:

We are deeply saddened by the killing of Qassim M. Aklan, a longtime employee of the U.S. Embassy in Sana’a. We condemn this vicious act in the strongest terms possible and extend our deepest condolences to his family and friends at this difficult time. Mr. Aklan, a Yemeni citizen, worked as a Foreign Service National Investigator at the Embassy for the last 11 years. He was a dedicated professional who will be greatly missed. We are coordinating closely with the Yemeni authorities to investigate this attack and to help bring those responsible to justice.

According to NYT, witnesses said that two men on a motorcycle drove up alongside the car of the embassy employee, Qassim M. Aklan, and one of them opened fire, killing him:

Mr. Aklan was in the west of the city; the embassy is in the eastern part. There was no immediate claim of responsibility, but militants have attacked official targets in Yemen in response to the government’s campaign against cells of the regional franchise, Al Qaeda in the Arabian Peninsula, which American counterterrorism officials have called the terrorist network’s most active affiliate.
[..]
Mr. Aklan had worked at the embassy for 11 years, she said, and was out with a family member when he was shot. In his most recent position at the embassy, he was employed as a security investigator and liaison, a fairly common position in American embassies that means he could have been doing work that involved background checks or coordinating with the local police.

Mr. Aklan (referred to as Qasim Aqlani in other reports) is what’s called a Foreign Service National Investigator (FSNI); there are no local officer positions in the Foreign Service.  Typically, here is what an FSNI does:

Performs all Regional Security Office responsibilities delegated to Post’s Foreign Service National Investigator’s (FSNI) Program. Carries out liaison functions with working level host country officials, and using all available information provides security advice to the senior FSNI if there is one or the Regional Security Officer.  Conducts locally employed staff and contractor background investigations, investigations related to terrorism, criminal activity, suitability and other issues in support of both Diplomatic Security and other USG law enforcement and security agencies. Assists in the coordination of VIP protection operations for assigned visits including liaison activities with all host government security elements during VIP visits such as POTUS and CODELS.

The AP reports that Yemeni President Abd Rabbo Mansour Hadi has said that “terrorists” were behind this assassination saying:

“Aqlani died as a martyr after terrorists killed him […]  The way he was killed reflects the barbarism and aggression of this outlawed group that is violating Islam and its principles that ban bloodshed.”

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Related articles

• Yemen says US embassy killing a terrorist act (gulfnews.com)
• US embassy security chief killed in Yemen (aljazeera.com)
• Yemen security chief at US embassy shot dead (telegraph.co.uk)
• U.S. Embassy Worker Killed In Yemen (outsidethebeltway.com)