LONDON -- An expensive and wide-ranging British investigation into alleged bribery by reporters crumbled Friday, after a jury acquitted four tabloid journalists of paying prison officers for information.

It was the latest in a string of cases where juries have failed to convict journalists who paid police, prison guards and other officials for stories. After the verdicts, prosecutors told most of the journalists facing upcoming cash-for-scoops trials that charges against them would be dropped.

Jurors at London's Central Criminal Court found Tom Wells, Neil Millard and Brandon Malinsky from the Rupert Murdoch-owned Sun and Graham Brough of the rival Daily Mirror not guilty of conspiring to commit misconduct in a public office.

Many journalists have been strongly critical of the prosecutions, saying reporters were being criminalized for seeking to uncover official secrets and wrongdoing.

"I've had nearly two years of torture," Malinsky said outside court, calling the prosecutions "a disgraceful waste of public money."

The charges were triggered by the 2011 revelation of illegal phone hacking at Murdoch's now-defunct News of the World tabloid.

After the scandal broke, several police investigations were launched into questionable tabloid practices, from eavesdropping on celebrities' voicemails to paying cash for tips.

Scores of journalists were arrested -- most of them employees of Murdoch's News Corp. -- though only a handful has been convicted of wrongdoing. The highest-profile casualty was former News of the World editor Andy Coulson, who was sentenced to 18 months in prison for conspiring to eavesdrop on mobile-phone voicemails.

More than 20 officials have also been convicted of leaking information, including details on Prince William and Prince Harry.

The Crown Prosecution Service said Friday that while it was right to prosecute officials "who flagrantly break the trust of the public ... the prosecution of journalists in these circumstances may not always be in the public interest."

Prosecutors said they were dropping charges against nine out of 12 journalists still facing trial -- including Coulson, who will no longer face retrial on a charge of paying police officers for royal phone directories.