A stinging report  by the Senate Intelligence Committee released Wednesday concluded that  the attack 16 months ago that killed four Americans in Benghazi, Libya,  could have been prevented, singling out the State Department for  criticism for its failure to bolster security in response to  intelligence warnings about a growing security crisis around the city. The  report is broadly consistent with the findings of previous inquiries  into the attack on Sept. 11, 2012, but it is the first public  examination of a breakdown in communications between the State  Department and the C.I.A. during the weeks leading up to the deadly  episode at the diplomatic compound where J. Christopher Stevens, the  American ambassador, died.
It is also the first report to implicitly criticize Mr. Stevens, raising  questions about his judgment and actions in the weeks before his death.  Like previous inquiries, the Senate investigation does not cite any  specific intelligence warnings about an impending attack.
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The report does not break significant new ground on the issue of  administration statements about the episode, or on the infamous “talking  points” drawn up after the attack for a television appearance by Susan  E. Rice, now the national security adviser. But it is unsparing in its  criticism of the State Department for failing to provide adequate  security to the mission even as violence spiked in Benghazi in June  2012. In contrast, the report said, the C.I.A. quickly bolstered  security at its annex about a mile away. 
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Together with the conclusions of previous investigations, the new Senate  findings are likely to increase pressure on Patrick F. Kennedy, the  under secretary of state for management, whose office oversees  diplomatic security. Republicans on the committee noted that Mr. Kennedy  held a similar job in the prelude to the bombings of two American  Embassies in East Africa in 1998 and should be held accountable for the  Benghazi tragedy. 
On  the contentious issue of the role of Al Qaeda or other international  terrorist organizations in the attack on the diplomatic mission, the  Senate committee’s report found that individuals “affiliated with” many  such groups had participated in the attack but that none of them  appeared to have planned or led the assault.
The  report found that among the many terrorist groups with which individual  attackers had some affiliation were Ansar al-Shariah, Al Qaeda’s North  African affiliate, Al Qaeda’s Yemen-based affiliate, and the Egyptian  network led by Muhammad Jamal. But the report said “intelligence  suggests that the attack was not a highly coordinated plot, but was  opportunistic.”
“It  remains unclear if any group or person exercised overall command and  control of the attacks or whether extremist group leaders directed their  members to participate,” the report said. “Some intelligence suggests  the attacks were likely put together in short order, following that  day’s violent protests in Cairo against an inflammatory video.”
The American-made video, which denigrated Islam and was posted on YouTube, set off a number of protests across the Middle East. 
An investigation published by The New York Times last month found that anger over the video had played a significant role in precipitating the Benghazi attack.
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At times Mr. Stevens requested additional security personnel from the  State Department in Washington. But the inquiry also found that in June  2012, around the time the threats were mounting, Mr. Stevens recommended  hiring and training local Libyan guards to form security teams in  Tripoli and Benghazi. The plan showed a faith in local Libyan support  that proved misplaced on the night of the attack. 
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After reading the cable, Gen. Carter F. Ham, then the commander of the  United States Africa Command, called Mr. Stevens to ask if the embassy  in Tripoli needed additional military personnel, potentially for use in  Benghazi, “but Stevens told Ham it did not,” the report said. A short  time later, General Ham reiterated the offer at a meeting in Germany,  and “Stevens again declined,” the report said.
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The  White House largely lined up behind the report’s findings. “This  reinforces what other investigations have found,” a White House  spokesman, Jay Carney, told reporters on Wednesday. 
The  State Department has been racing to fulfill 29 recommendations made in  December 2012 by an independent review panel as part of its  investigation into the attacks. Those include sending dozens of  additional diplomatic security agents to high-threat embassies and  installing millions of dollars in advanced fire-survival gear.