London (CNN) -- The editor of Britain's Daily Mirror told a press ethics investigation Monday that he had no knowledge of phone hacking at the tabloid, though it "might well have" taken place at the tabloid newspaper without his knowledge.
Richard Wallace made the comments under questioning by lawyer David Barr at the ongoing Leveson Inquiry, a wide-ranging government-backed investigation of British press ethics and practices.
James Hipwell, a former employee of the Daily Mirror, testified last month that phone hacking "happened every day" at the Mirror's show business desk in late 1999, though he provided no specific evidence. In a separate case, Hipwell was convicted in a stock-tip scandal in 2005.
Wallace was the show business editor at the paper from October 1999 to October 2000.
Barr pressed Wallace on Hipwell's testimony, asking him whether the allegations of phone hacking were true.
"No, not to my knowledge," Wallace said.
Barr followed up by asking whether it was "possible it was going on, but being hidden from you?"
Wallace responded: "It might well have been."
When asked about the paper's revealing of a celebrity affair in 2002 while he was the head of news, Wallace said, "it's possible" the tip about the affair may have come from intercepted voice mail messages -- again without his knowledge.
"I don't recall the exact nature of (the source)," Wallace said, adding, "It could have come from anywhere, really."
The period of time in question occurred during Piers Morgan's tenure as editor of the newspaper. Morgan, now a CNN anchor, left the paper in 2004; Wallace replaced him as editor.
Hipwell said in his December testimony that he "cannot prove" that Morgan knew about illegal eavesdropping, but that it was "very unlikely he did not know what was going on."
Morgan has vigorously denied ordering phone hacking at any point during his career.
Morgan testified at the inquiry last month that he did not believe phone hacking had taken place when he was editor of the tabloid.
Speaking by video link, he tenaciously defended himself against accusations that he knew more about phone hacking.
The Leveson Inquiry was prompted by public and political outrage at the revelation that another tabloid, Rupert Murdoch's News of the World, hacked into the phone of a missing teenage girl who later turned out to have been murdered.
Murdoch's son James ordered the best-selling paper closed over the scandal.
Much of the inquiry -- and a related police investigation -- focus on allegations of phone hacking by the News of the World.