Andy Coulson, a former editor of The News of the World Sunday tabloid who went on to become Cameron's communications director, testified Thursday before the Leveson inquiry.
Coulson said he told Cameron in 2007, before he took the post as head of communication for the Conservative Party, that he had no knowledge of phone hacking at the newspaper.
The Guardian said the panel Thursday did not question Coulson further on phone hacking because he has been arrested in relation to ongoing police inquiries into the alleged phone hacking. The panel is not allowed to ask questions that could prejudice any subsequent trial, The New York Times said.
Coulson resigned from his government post after the phone hacking scandal went public. The Times said Cameron has tried to distance himself from his former aide, saying he would not have hired him in hindsight.
The Times said the hearings are being watched closely to determine if media mogul Rupert Murdoch's staff had any influence on Britain's political elite.