RIYADH, Saudi Arabia -- With the kidnapping of an American and threats to inflict on him the same degrading punishments seen at Iraq's U.S.-run Abu Ghraib prison, suspected al-Qaida terrorists appear to have unleashed a new tactic in their violent drive against Saudi Arabia's rulers.
Saudi authorities searched Sunday for Paul M. Johnson, an American who was apparently abducted by militants who claim responsibility for gunning down another American in Riyadh.
It was the third killing of a Westerner in the Saudi capital in a week, part of a stepped up campaign aimed at driving out foreigners and sabotaging the oil sector, key to the Saudi economy and basis of the rule by the kingdom's royal family.
The U.S. Embassy warned Americans slain over the past week were first extensively shadowed before being targeted.
Kenneth Scroggs was shot in the back as he parked in the garage at his home on Saturday. Last Tuesday, Robert Jacobs was also killed in his parking garage.
The killings "involved extensive planning and preparation," a U.S. Embassy warden message said. "Often, this pre-attack surveillance can be detected."
Al-Qaida, led by Saudi-born Osama bin Laden, often rails against Saudi Arabia's rulers for their close links to the United States.
"The Saudis know that this is an enemy that is coming after them. The killing of foreigners ... is a direct attack against the Saudi regime," U.S. Secretary of State Colin Powell said on ABC's "This Week."
Powell said Saudi leaders are mobilizing all resources against militants but added, "I think that there is more that they can do."
The Saudis can "build up their forces" and cut off funding for militants, he said on "Fox News Sunday." "There's probably more we can do with respect to intelligence exchange, and we are working at all of these," he said.
Prince Bandar, the Saudi Ambassador to the United States, called the attacks on Americans "craven acts of evil."
"Their intention is to shake our will, to frighten away our friends and allies, and to undermine our society," Bandar said.
None of the gunmen have been caught in this week's fatal shootings of the two Americans and, on June 6, Irish cameraman Simon Cumbers.
Saudi security officials, speaking on condition of anonymity, said police stormed a suburban Riyadh house Sunday morning, arresting a man inside and confiscating a computer. It wasn't clear whether he was linked to any of the past week's shootings.
The purported al-Qaida statement, posted late Saturday on an Islamic Web site, threatened to treat Johnson, the abducted American, as U.S. troops treated Iraqi prisoners -- a reference to sexual and other abuses at Abu Ghraib prison in Iraq.
It showed Johnson's passport and a Lockheed Martin business card bearing his name. The passport said Johnson was born in New Jersey. His son Paul Johnson III said his father moved to the kingdom in 1983 to work for Lockheed Martin.
The al-Qaida statement said Johnson is one of four experts in Saudi Arabia working on developing Apache attack helicopter systems.
"Everybody knows that these helicopters are used by the Americans, their Zionist allies and the apostates to kill Muslims, terrorizing them and displacing them in Palestine, Afghanistan and Iraq," said the statement. It said al-Qaida would release a videotape later with Johnson's confessions and its demands.
A car belonging to Johnson was found Saturday near Imam University, security officials said. Saudi press reports said the car was booby-trapped and later caught fire. The university is about 12 miles from the neighborhood where Scroggs was shot.
Lockheed Martin issued a statement confirmed that Johnson was missing. The U.S. Embassy said it was working with Saudi officials to find the kidnapped American.
Paul Johnson III, of Port. St. John, Fla., asked the kidnappers to let his father go.
"He doesn't deserve it. It's not his fault he's over there. It's his job," he said on NBC News.
He said his father had been nervous about being in Saudi Arabia. "My dad's probably praying, wondering how he got himself into this and how he can get himself out," he said.
The militant attacks against Westerners, government targets and economic interests in the kingdom have surged despite a high-profile campaign against terrorists the government began after suicide bombings last year.
Terror experts have noted that the militants are using several tactics -- including shootings and ambushes where the gunmen do not die -- rather than limiting themselves to suicide bombings or swift attacks under the cover of darkness.
The statement claiming Saturday's shooting and kidnapping was signed by al-Qaida in the Arabian Peninsula, the same group that claimed responsibility for a May 29-30 shooting spree and hostage-taking in the eastern Saudi oil hub of Khobar that killed 22 people, most foreigners.
Saudi security arrested one attacker in Khobar, but three others escaped.
Saudi Arabia relies heavily on a foreign work force. An estimated 8.8 million foreigners work among 17 million Saudis in the kingdom, some in the oil sector, banking and other high-level businesses, but the majority in service-industry jobs such as maids, bell boys or taxi drivers.
The U.S. Embassy had already advised Americans to leave the kingdom, and the British Embassy on Sunday said it was authorizing the voluntary departure of nonessential staff and their families.
Meanwhile, several Islamic Web sites were carrying links to a videotape -- also purportedly from al-Qaida -- that claims to show last Tuesday's killing of Jacobs, 62, of Murphysboro, Ill., who worked for U.S. defense contractor Vinnell Corp.
The video, less than two minutes long, does not show any faces. It begins with men running in a garage and a voice yelling in English, "No, no, please!" A shot is fired, and the body of what appears to be a Western man falls to the ground. Two gunmen fire at least 10 more shots at the fallen man, then one kneels by his head and motions as if he is beheading him.