(CNN) -- The deadly attack on the U.S. diplomatic compound in Benghazi, Libya, was "likely preventable" based on known security shortfalls and prior warnings that the security situation there was deteriorating, the majority of the Senate Intelligence Committee concluded in a report released on Wednesday.
Separately, the findings also noted what the FBI had told the panel -- that 15 people cooperating with its investigation had been killed in Benghazi, undercutting the investigation. It was not clear if the killings were related to the probe.
Moreover, it said that people linked with various al Qaeda-related groups in North Africa and elsewhere participated in the September 11, 2012, attack, but investigators haven't been able to determine whether any one group was in command.
The report placed some blame for the outcome on the State Department, saying it should have "increased its security posture more significantly" in Libya's second-largest city because of general warnings that U.S. personnel were at risk.
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