WASHINGTON — The CIA’s insistence that it did not spy on its Senate overseers collapsed Thursday with the release of a stark report by the agency’s internal watchdog documenting improper computer surveillance and obstructionist behavior by CIA officers.

Five agency employees – two lawyers and three computer specialists– improperly accessed Senate intelligence committee computers earlier this year in a dispute over interrogation documents, according to a summary of a CIA inspector general report describing the results of an internal investigation. Then, despite CIA Director John Brennan ordering a halt to that operation, the CIA’s office of security began an unauthorized investigation that led it to review the emails of Senate staffers and search them for key words.

After Senate leaders learned about the intrusion in January and objected, the CIA made a criminal referral to the Justice Department, alleging improper behavior by Senate staffers when they took the internal CIA review documents. That referral, CIA watchdog David Buckley found, was based on inaccurate information and was not justified.

Brennan also asked his agency’s inspector general to examine whether the CIA committed wrongdoing. When internal investigators interviewed the three CIA computer specialists who helped access the Senate machines, they exhibited “a lack of candor,” the IG report said, suggesting an attempt to cover up their actions.

Those internal conclusions prompted CIA Director Brennan to abandon months of defiance and defense of the agency and apologize to Senate Intelligence Committee leaders.

“The director said that wherever the investigation led, he would accept the findings and own up to them,” said his spokesman, Dean Boyd.

Brennan has convened an internal accountability board chaired by former Sen. Evan Bayh, D-Ind., to examine whether any CIA officers should be disciplined. Furious Democrats demanded further investigation and a public accounting from Brennan. Sen. Mark Udall, D-Colo., called for the director’s resignation, citing “a tremendous failure of leadership.”

At issue is a search by agency officers for information gathered in the course of a Senate investigation into the CIA’s interrogation techniques.