Sources close to the investigation said a federal prosecutor who headed the ‘’exhaustive investigation’’ to the destruction of the interrogation tapes filmed at secret prisons concluded there just wasn’t enough evidence to bring an indictment.

The statute of limitations on criminal law covering the tapes’ November 2005 destruction expired this week, making future prosecution impossible.

But part of the nearly 3-year-old criminal investigation that examines whether US interrogators went beyond the legal guidance given them on the rough treatment of suspects will continue, a Justice Department official told reporters.

The potentially more explosive investigation will examine whether CIA employees and contractors broke the law in conducting interrogations at “black site” prisons.

The interrogations were conducted in the months following the Sept. 11, 2001, attacks in the US.

In his newly released memoirs, former President Bush writes that the personally authorized the CIA to use the techniques in 2002, after obtaining assurances from the government lawyers that the interrogation program would be lawful.

Bush’s memoirs have also caused heartburn with some British officials who said Tuesday there was no evidence to support claims by Bush in his book that information extracted by “waterboarding” saved British lives by foiling attacks on Heathrow airport and Canary Wharf. The practice is condemned by Downing Street as torture.

When the investigation began, then-CIA director Michael Hayden said the tapes had been destroyed to protect the identities of the intelligence agents who interrogated the terror suspects.

But some US legislators and international rights campaigners dismissed the explanation, saying the tapes’ destruction was meant to cover up alleged torture of detainees.

“This decision is stunning: There is ample evidence of a cover-up regarding the destruction of the tapes,’’ ACLU Executive Director Anthony D. Romero said. “The Bush administration was instructed by a court of law not to destroy evidence of torture, but that’s exactly what it did.’’

The tapes showed the interrogations of two high-profile detainees.

Sources have said they depicted waterboarding, a form of simulated drowning that human rights groups and Obama administration officials say is torture.

The tapes allegedly showed the waterboarding of two suspects, Zayn al-Abidin Muhammed Hussein, an alleged facilitator of terrorism better known as Abu Zubaida, and Abd Al-Rahim Al-Nashiri, a Saudi suspected of involvement in the October 2000 bombing of the USS Cole as it docked for refueling in a Yemeni port.

Sources have said authorities found it difficult to pinpoint the motivation for destroying the tapes, and that it was difficult to prove criminal intent.

CIA officials have long said the motive was innocent: After the emergence of widely reviled images of detainee abuse at the Abu Ghraib prison in Iraq, CIA veterans feared that disclosing the videotapes could put the interrogators’ safety at risk if their identities became known.

Jose Rodriguez, a top CIA official from 2004 to 2007, authorized the tapes’ destruction and has been a key focus of the inquiry. Sources said Tuesday that he will not be charged.

Meanwhile, CIA Director Leon Panetta said the agency’s Office of Security will “fully investigate” the WikiLeaks documents released on a public web site.

“In some cases, CIA sources and methods have been compromised, harming our mission and endangering lives,” he said.

In an internal memo, released to the media Monday, the director said that sharing information “cannot extend beyond the limits set by law and the ‘need to know’ principle. The media, the public, even former colleagues, are not entitled to details of our work.”

Panetta added that the leaks had potentially done “incredible damage to our nation’s security and our ability to do our job of protecting the nation. More importantly, it could jeopardize lives. For this reason, such leaks cannot be tolerated.”