The CIA inspector general shared his findings with the Justice Department, which has so far declined to pursue criminal charges against the CIA employees, officials said.
The inspector general concluded "that some CIA employees acted in a manner inconsistent with the common understanding reached between" the Senate Intelligence Committee and the CIA in 2009 regarding access to a shared classified computer network, Boyd said. The shared network had been used by Senate aides to access classified files on CIA interrogations. The CIA penetration occurred after the aides got ahold of documents that the CIA claimed were internal, but which showed that some CIA officials shared misgivings about the treatment of al Qaida detainees.
Brennan informed Senate intelligence committee Chairwoman Dianne Feinstein and Sen. Saxby Chambliss, the senior Republican on the committee, "and apologized to them for such actions by CIA officers as described in the (inspector general's) report," Boyd said.
Feinstein said the probe proved what she announced in an unusual, long speech on the Senate floor in March, that the computers were searched "in violation of an agreement we had reached, and I believe in violation of the constitutional separation of powers."
The apology was a turnabout for the CIA director, who until this week had dismissed the notion that the CIA did anything wrong.
After Feinstein complained about the CIA's penetration of committee computers, Brennan said, "When the facts come out on this, I think a lot of people who are claiming that there has been this tremendous sort of spying and monitoring and hacking will be proved wrong." He added, "CIA hacking into, you know, Senate computers, nothing could be further from the truth. I mean, we wouldn't do that."
By all accounts, the spying flap and the larger dispute over decade-old CIA practices have poisoned relations between Senate Democrats and the CIA.
On Thursday, Democrats pressed Brennan to publicly apologize.
"I am concerned about the director's apparent inability to find any flaws in the agency he leads," said Sen. Mark Udall, D-Colorado. "I also believe the administration should appoint an independent counsel to look into what I believe could be the violation of multiple provisions of the Constitution as well as federal criminal statutes..."
The CIA released few details about the investigation by agency inspector general David Buckley. Sources on each side of the dispute, who spoke on condition of anonymity because they were not authorized to go beyond official statements—offered divergent descriptions of its findings.
Senate aides familiar with the matter say the CIA used classified "hacking tools" and created a fake user account in an effort to retrieve documents the CIA believed the Senate staffers had improperly accessed.
A U.S. official familiar with the inspector general report disputed that hacking tools were used, and said that there was no malicious intent behind the CIA actions, but simply an effort to account for documents believed to have been improperly accessed.
At the White House, spokesman Josh Earnest defended Brennan, pointing out that the CIA director John "is the one who suggested that the inspector general investigate in the first place," and saying he continued to enjoy the president's confidence.