NEW YORK - A new book brings to a wider audience a theory of cover-up, sweeping blame and staggering security failures behind the 2007 assassination of former prime minister Benazir Bhutto.

Author and Chilean diplomat Heraldo Munoz headed a damning UN report in 2010 that said Benazir Bhutto's death could have been prevented and that Pakistan deliberately failed to investigate properly.

Now a UN assistant secretary general, his book "Getting Away with Murder: Benazir Bhutto's Assassination and the Politics of Pakistan", goes on sale in the United States next week.

Oxford-educated Benazir served twice as prime minister and had returned from exile to stand in elections when she was killed in a gun and suicide attack on December 27, 2007.

Six years later, no one has been convicted of her murder.

The government at the time blamed the Taliban. Despite scant evidence, a court this August charged Pervez Musharraf with her killing.

Munoz compares the assassination to a collective murder plot in a 17th century play and singles out Pakistan's ex-interior minister in particular for refusing to give straight answers.

Asked at a New York launch event whether he feared for his life during his investigation, Munoz said "not really", but revealed that in around January 2010 he was forced to step up security.

"I got a warning from a very trustworthy source that 'these people' are capable of anything and 'these people' don't know the world," he told the audience.

Although he never knew who "these people" referred to "I thought maybe we were stepping on some toes," he said.

Munoz likened the best explanation for who killed Benazir to the 17th century Spanish play "Fuenteovejuna" by Felix Arturo Lope de Vega, in which a village united together to kill a hated commander.

Al-Qaeda wanted her dead, the Pakistani Taliban executed the attack - possibly with support of rogue intelligence agents - and local police did a cover-up, Munoz said.

Benazir's own security failed her and those who encouraged her to return to Pakistan did not provide her with protection, Munoz argues.

At one point the US suggested she hire the security contracting firm formerly known as Blackwater, Munoz said, but Musharraf refused to let foreign agents in.

"Political actors, even those close to her, would rather turn the page rather than find out who did it," he said.

"She was clearly a target for the Pakistani Taliban and Al-Qaeda for sure," said Munoz. "Sectors of the Pakistani establishment also wanted her dismissed or dead."

He said police were "clearly responsible for a cover-up and I'm convinced that came from higher up".

Federal investigators were delayed in accessing the scene, first by cups of tea until it got too dark and then by a big lunch.

In the end they collected only 23 pieces of evidence from the washed-down scene where Britain's Scotland Yard said ordinarily thousands would have been expected.

Munoz said it was ridiculous to imagine that Benazir's widower, Pakistan's desperately unpopular former president Asif Ali Zardari, had been involved in her death. "He was helpful but I cannot say his whole government was helpful because we encountered all sorts of obstacles," he said.

He said former interior minister Rehman Malik, Benazir's head of security, had been in a back-up bullet-proof Mercedes but was nowhere to be found immediately after the attack.

"They probably wanted to save their skin, to put it bluntly," Munoz said. "Never could we get straight answers from him."

The diplomat said guilt was for the courts to decide, but that Musharraf bore "political responsibility" by not providing adequate security to a former prime minister living under threat.