(CNN) -- News Corp. Chairman Rupert Murdoch is apologizing for secretly recorded criticism of police investigations into his newspapers, but he says he's still frustrated by the extent and length of the probes.
Wednesday's apology came in letters to two separate British Parliament committees investigating the allegations. Murdoch was heard on the tape saying the police are "totally incompetent" and that "it was a mistake" for his company to cooperate with the police.
Murdoch is also heard saying, "It's the biggest inquiry ever, over next to nothing."
London's Metropolitan Police Service is running parallel investigations into phone-hacking by British journalists and alleged payments for newspaper stories involving the royal family.
The scandal began with allegations of phone-hacking at Murdoch's popular Sunday tabloid, News of the World.
The secret recording of Murdoch, apparently made by an employee in March, was published this month by an investigative journalism website, Exaro News, and later broadcast by Britain's Channel 4 News. CNN has not independently confirmed the authenticity of the recording, but News Corp. has not disputed it, and Murdoch references his comments several times in his letters.
The recording prompted the House of Commons Culture, Media and Sport Committee and the Home Affairs Select Committee to ask Murdoch to explain his comments.
Murdoch's letter to the Home Affairs committee was sent Wednesday and made public Thursday by Chairman Keith Vaz.
"Obviously we did not treat any of this alleged wrongdoing as 'nothing,'" he wrote to Vaz. "I did not intend to suggest that any violations of the law are tolerable or acceptable."
Murdoch says he "used the wrong adjectives" to voice his frustration over the investigations but was upset by the impact on his employees.
His employees, he says, described pre-dawn raids by as many as 14 police officers investigating elements of the scandals. They said they were "left in limbo" for as long as a year and a half while waiting to hear about charges, and he said there have been "suicide attempts and medical conditions" as a result of the stress on employees and their families.
"While I regret my choice of words in that highly emotional meeting, I care deeply about our employees," Murdoch writes.
Vaz also asked Murdoch to explain why he said it was a "mistake" to hand over so many documents to investigators, and why he is now requiring police to obtain court orders for further files.
Murdoch responds that his company has extensively cooperated with police, first volunteering "a mountain of evidence" to investigators and then satisfying 98% of their 1,900 follow-up requests.
"Where it appears that requests were unreasonable or in pursuit of materials already provided, we have asked the (police) to reconsider," Murdoch writes.
He says he should never have called the police incompetent and says he actually views their investigations as thorough to the point of being excessive.
"That said," Murdoch writes, "my personal view is that this has gone on too long."
Vaz said Thursday he welcomes Murdoch's apology and explanation of his comments.
"Mr. Murdoch's letter does raise the issue of the length of time these investigations have taken which the Home Affairs Committee has raised in the past and which have so far cost the taxpayer £20.3 million ($30.9 million)," Vaz writes.
Murdoch appeared before the Culture, Media and Sport Committee two years ago to give evidence on the phone-hacking scandal, telling them it was "the most humble day of my life."
News International was forced to close the 168-year-old News of the World, its best-selling Sunday tabloid, that year amid anger over allegations an investigator working for the paper had hacked the voice mail of a missing 13-year-old girl, Milly Dowler, who was later found murdered.
Since then, a number of former News International staff have been charged with criminal offenses and await trial.
They include Rebekah Brooks, the former News of the World and Sun editor who served as chief executive of News International from 2009 to 2011, and former News of the World editor Andy Coulson, who went on to work for Prime Minister David Cameron but later resigned. They deny wrongdoing.
Several Sun journalists have also been charged in connection with the investigations.