Two newspapers on opposite sides of the Atlantic were instrumental in cracking open the massive phone-hacking scandal in Rupert Murdoch’s British media empire. And they might not have been able to do so without a little Anglo-American cooperation.

The New York Times and the Guardian newspaper both landed major scoops on the story that propelled the latter to global status. Reporters from the two papers mostly worked independently, competing against one another to get to the bottom of corruption at Murdoch’s News of the World tabloid and within the British police force.

But the story might not have happened at all without a phone call early last year from Guardian editor Alan Rusbridger to his counterpart at the Times, Bill Keller.

Rusbridger told Keller that he was frustrated. At the time, the Guardian was the only major British news organization still pursuing the hacking story, which seemed to have died with the closing of the official police investigation in 2007.

News Corp. officials had repeatedly and publicly dismissed the Guardian’s revelations, such as legal settlements paid to hacking victims, as the work of a business competitor and political rival. (The Guardian generally supports Labor, the party of former prime ministers Tony Blair and Gordon Brown; Murdoch has more often backed the Conservatives, the party of the current prime minister, David Cameron.)

What’s more, some of the Guardian’s reporting avenues were cut off by British laws that limit the extent of press inquiries in cases under police investigation; one key figure in the scandal, a private detective named Jonathan Rees, was being investigated on murder charges, hampering the Guardian’s efforts to probe his activities.

Perhaps the Times would be interested in taking a look at the News Corp. scandal, Rusbridger asked?

Keller was intrigued. “I’d been watching the hacking story from afar, and it seemed like a good time to bring this amazing yarn to the attention of American readers,” Keller said Wednesday via e-mail, “especially if there were fresh angles to be explored.”

The Times editor has denied that the paper’s initial coverage of the story was an attempt to embarrass News Corp. at a time when the Murdoch-owned Wall Street Journal had started a New York edition in direct competition with the Times.

Keller assigned three investigative reporters — Don Van Natta Jr., Graham Bowley and Jo Becker, who had won a Pulitzer Prize while working at The Washington Post — to meet with Rusbridger and Nick Davies, the Guardian’s lead reporter on the story.

After a meeting in London, the Times reporters spent five months reporting and writing their article. Despite stonewalling by Scotland Yard (the paper’s formal request for official documents still has produced nothing), a 6,000-word piece published last September in the New York Times Magazine broke new ground.

It revealed that the phone hacking had involved many more people than News Corp. had previously acknowledged, including former News of the World editor Andy Coulson, by then a media adviser to Cameron. It found that Scotland Yard had closed its investigation prematurely, despite collecting evidence indicating that the tabloid was “routinely listening in on [British] citizens.”

The Times story led to a new police inquiry and a revival of interest by Britain’s media, which began a steady drip of articles mapping the contours of corruption among Murdoch’s powerful British media interests and the nation’s political establishment and police force. The pressure led Coulson to resign from Cameron’s office in January. The article also drew attention Wednesday during a session of Parliament.

But the hacking story didn’t truly detonate until July 4, when the Guardian published a shocking development. Davies and colleague Amelia Hill reported that News of the World had intercepted desperate voice mails left by family members on the phone of Milly Dowler, a 13-year-old girl who disappeared in March 2002 and was later found dead.

The public condemnation, and demand for answers, grew deafening — “a giant heave of revulsion,” in Rusbridger’s words.

In rapid succession, Murdoch closed the 168-year-old News of the World and dropped its multibillion-dollar bid for a British satellite TV company. Police arrested Coulson and his predecessor at the tabloid, Rebekah Brooks, and top officials at Scotland Yard resigned. The scandal is still rattling Cameron’s government, largely on the strength of transatlantic tag-teaming by two newspapers.

The two papers’ close working relationship grew late last year when they collaborated on the story of thousands of leaked military reports and diplomatic memos released by the Wikileaks group.

In the Wikileaks case, the Times and the Guardian were part of a consortium of media outlets chosen by Wikileaks leader Julian Assange to receive large caches of leaked documents. After the initial release, Assange was angered by a Times story about him and refused to release subsequent troves of documents to the newspaper, according to people at the Guardian. The Guardian stepped in to help, passing the documents to the Times without Assange’s explicit approval.

Keller and Rusbridger stressed that the two news organizations had a more independent relationship on the hacking story.

“You should be clear that we put nothing in the paper — not one factoid — that we had not reported on our own,” Keller said. “That meant re-reporting a fair amount of material the Guardian had already reported.” The Guardian, he says, “did strong, tenacious reporting,” but the Times reporters developed their own sources and did their own legwork. “I don’t mean to steal the Guardian’s thunder, but we made a real difference on this story,” Keller said.

Rusbridger, too, is at pains to declare the Guardian’s work its own. He said in an e-mail from London on Wednesday that his paper had been on its own for months. “Nick Davies and I gave the Times reporters some initial help in understanding the story and the background to it,” he wrote. “After that they went their own way. “

The British editor took a more triumphant tone in an essay for Newsweek about his paper’s role. Before the Guardian’s revelation about Milly Dowler, he wrote, “you needed Murdoch to get elected in Britain — or so most politicians believed. And — always unspoken — Murdoch needed certain things, too. It wasn’t necessarily corrupt. But it was certainly corrupting. And now — with one story and one unanimous vote in the House of Commons [for a full investigation] — that spell has been broken.”