"You crusaders have gathered against the Muslims, and killed the old and the children, and raped women, and stolen the money and fortunes of Muslims," the voice declared.
Al-Muqrin and three other Al-Qaeda militants were killed in a raid by Saudi security forces on 18 June. The raid came shortly after al-Muqrin's group -- calling itself Al-Qaeda in the Arabian Peninsula -- posted an Internet video of the beheading of U.S. hostage Paul Johnson.
Saudi authorities hailed the killing of al-Muqrin and his associates as a major blow to the terror network in the desert kingdom.
They said the four militants played key roles in a recent wave of attacks aimed at driving from the country thousands of foreigners or "infidels" -- most of whom work in the oil industry -- in a bid to topple the ruling royal family.
"From the Saudi perspective, they feel that they have basically eliminated the core of four cells and most of up to six cells -- and that much of the active leadership and sort of trained manpower for Al-Qaeda has now been decimated," said Anthony Cordesman, a leading U.S. analyst of the Middle East, military affairs, and terrorism with Washington's Center for Strategic and International Studies.
Like many experts, Cordesman said he's encouraged by the Saudi response to the recent attacks, the worst of which was in the oil city of Khobar on 29 May. Twenty-two people were killed in the shooting rampage and hostage saga. Al-Muqrin claimed responsibility for that attack.
The terrorism crisis in Saudi Arabia began in May 2003, when militants bombed a complex housing mostly foreigners in Riyadh, killing 35 people and wounding 200.
Cordesman said it would be premature to conclude that the latest strikes against Al-Qaeda have dealt a death blow to that campaign on the Arabian peninsula.
"There is a vast range of potential uncertainty. The Saudis may be correct. They may have been able to deal with the most serious cells. But on the other hand, they didn't anticipate the threat that began in May 2003; they didn't properly characterize it then. And the United States and many other countries have found that it's very easy to say that you've dealt with a terrorist movement, and then find that you really haven't; that it mutates, evolves and new terrorists emerge," Cordesman said.
Almost as soon as al-Muqrin's death was announced, Al-Qaeda websites in Saudi Arabia said the group already had a new leader: Salih Muhammad Awadallah al-Alawi al-Oufi, reportedly a former member of the Saudi military and police forces.
The quick turnaround is an example of why experts like Marc Sageman believe Saudi Arabia is likely to continue to face attacks from militants intent on bringing down the House of Saud.
Sageman, a University of Pennsylvania professor, is a forensic psychiatrist and author of the recent book "Understanding Terror Networks." He told RFE/RL that Al-Qaeda should not be thought of as a hierarchical organization but as a social movement based on a set of ideas.
He said following the blow to the network in Saudi Arabia, a pattern is likely to emerge similar to what happened after the United States attacked infrastructure and leaders of the group following the 11 September 2001 attacks on America.
Sageman said that before 9/11, with its leadership intact, Al-Qaeda operations were big, carefully planned and carried out by well-trained operatives. Afterward, Sageman said, Al-Qaeda attacks around the world became smaller in scale, but more numerous and more reckless.
"It's very similar to what we have in the United States as a war on drugs, where you arrest the local drug dealer at the street corner and you create a gap where you have an intense competition and usually the most aggressive person wins. So you breed more aggressive, less well-trained, but more reckless leadershipm," Sageman said.
A recent study by Cordesman suggests there are an estimated 15,000 to 25,000 men in Saudi Arabia who have had some kind of training in terrorist camps -- many of them in Afghanistan, such as al-Murqin. Still, Cordesman said it is far from clear what connection any of these people may now have with Al-Qaeda militants.
Cordesman and Sageman both noted that southern Saudi Arabia also represents a likely source of new militants, many of whom are believed to filter in from bordering Yemen.
Adel al-Jubeir, an adviser to Saudi Crown Prince Abdullah, told reporters in Washington on 19 June that there are 15,000 security officers scouring the country in search of militants.
"We are not fighting this war for public relations purposes. We are fighting this war to ensure the safety and security of our citizens and our residents. People in Saudi Arabia are being murdered. We have every intention of stopping those murders," al-Jubeir said. "We do it for our sake."
But Sageman believes Saudi efforts in what he called "the war of ideas" are equally important. He said that since Al-Qaeda is mainly a social movement based on ideas, Saudi authorities must continue to challenge those ideas by stopping radical clerics from inciting followers to violence.
"They've tried to rally the imams to argue that the Al-Qaeda version or interpretation of the Koran is not legitimate, it's a distortion of the Koran. And they even got inspiring imams that have been long associated with Al-Qaeda to show revulsion to what happened with the beheading of Mr. Johnson, and have criticized Al-Qaeda this past weekend. This is unique, but it shows that the Saudi authorities really understand what is going on here," Sageman said.
Sageman said the general Saudi reaction to the beheading of Johnson and other Western hostages in the Muslim world has been negative. He said militants may be overplaying their hand, horrifying a lot of people who might otherwise be sympathetic to their cause.
Another aspect of the war of ideas, Sageman said, is the Saudi government's attempt to slowly open up the political system and introduce liberal reforms to society. Most of this has been rhetoric, but the effort aims to address a key source of disaffection -- people who feel shut out of the political process.
But in signaling an openness to reform, the royal family is walking a tightrope. Its chief claim to legitimacy is as the keeper of a purportedly purer form of Islam -- Wahhabism -- and protector of Islam's two holiest sites in Mecca and Medina.
Sageman said the need to reform and the need to retain such legitimacy represent a major dilemma for the royal family. The more the Saudi government accepts reforms, the more vulnerable it will become to militants' claims that it has betrayed Islam -- a factor which could continue to make it a target for attacks.
"This is going to be a long process," Sageman said. "This is just, I think, the first salvo of a fairly long process. I'm afraid that in Saudi Arabia, terrorism has basically become an insurgency."