Hewlett Packard (HP)has been heavily criticised by US members of Congress at a hearing into corporate spy tactics at the computer and printer maker.
Patricia Dunn was one of the few people willing to testify
The House of Representatives Energy and Commerce subcommittee said HP had scant legal backing for spying on staff and obtaining journalists' phone records.
One member of the subcommittee compared it to the Watergate scandal.
HP chief executive Mark Hurd later gave a "heartfelt apology" for what he said had been "a rogue investigation".
"I wish I had asked more questions. There are signs I wish I had caught," he said.
In an attempt to discover which employee had leaked "confidential" reports to the press, investigators obtained the phone records and other data of journalists and HP employees without their permission.
The practice - known as "pretexting" - is a common one among private investigators but tests the limits of California state laws, as prosecutors believe it violates laws covering identity theft and unauthorised access to computer data.
Congressman John Dingell of Michigan described it as "a plumbing operation that would make Richard Nixon blush".
Other members of the committee questioned why so many of those involved in the scandal had invoked their right not to testify at the hearing.
One of those, HP's top lawyer, quit her post hours before the hearing.
It later emerged at the hearing that Ann Baskins, who had worked for the company for 24 years, was given a $3.6m (£1.9m) payment when she left.
Ann Baskins had worked for Hewlett Packard for 24 years
Ms Baskins, two other former HP executives and a number of hired investigators were among ten people who chose not to answer questions.
Former chairwoman Patricia Dunn, who resigned because of the scandal, said she had relied on assurances from investigators that the information they obtained was done so legally.
"I deeply regret that so many people, including me, were let down by this reliance on such advice," Ms Dunn said.
But she added: "I do not accept personal responsibility for what happened."
The US Justice Department and California's attorney general are also investigating the company.