Riyadh, Saudi Arabia ? An al-Qaida cell beheaded American engineer Paul M. Johnson Jr., and in a swift retaliation, officials said Saudi security forces tracked down and killed the leader of the terrorist group in a shootout Friday.

Johnson, who was kidnapped last weekend, was the latest victim of an escalating campaign of violence against Westerners that aims to drive foreign workers from the country and undermine the ruling royal family, hated by al-Qaida.

The death hours later of Abdulaziz al-Moqrin, the reputed leader of al-Qaida in the kingdom, was a coup for the Saudi government, which has been under intense pressure to halt the wave of attacks. In a video posted Tuesday on the Internet, a hooded al-Moqrin held an assault rifle and shouted demands for the release of al-Qaida prisoners as Johnson sat blindfolded.

Saudi forces killed four other al-Qaida militants in Friday’s shootout, which came after a witness reported the license plate number of a car from which the militants dumped Johnson’s body and police then stopped the vehicle at a gasoline station, security officials said.

But they were too late to save Johnson, whose severed head was shown Friday on a Web site. The photographs and a statement, in the name of Fallujah Brigade of al-Qaida in the Arabian Peninsula, appeared after Johnson’s wife went on Arab television and tearfully pleaded for his release.

“In answer to what we promised … to kill the hostage Paul Marshall (Johnson) after the period is over … the infidel got his fair treatment,” the al-Qaida statement said.

“Let him taste something of what Muslims have long tasted from Apache helicopter fire and missiles,” the statement said.

Johnson, 49, worked on Apache attack helicopter systems for Lockheed Martin. His captors had threatened to kill him by Friday if the kingdom did not release its al-Qaida prisoners. The Saudi government rejected the demands.

Tearful remembrances

President Bush said the execution showed “the evil nature of the enemy we face.”

“They’re trying to get us to retreat from the world,” Bush said. “America will not retreat. America will not be intimidated by these kinds of extremist thugs. May God bless Paul Johnson.”

Johnson’s family in Galloway Township, N.J., said authorities worked as hard as they could to rescue him, and that his slaying did not dampen their respect for his adopted country.

“Paul considered Saudi Arabia his home. He loved the people and the country,” said an FBI agent speaking on behalf of Johnson’s relatives.

“They also know this act of terrorism was committed by extremists and does not represent the Saudi Arabia that Paul often spoke and wrote about to his family,” said Joseph Billy Jr., special agent in charge of the FBI’s Newark office.

John Hayes, a childhood friend of Johnson’s, was overcome with emotion.

“It’s just unbelievable. He didn’t deserve that,” said Hayes, 50. “This man wasn’t even fighting a war over there.”

Riyadh shootout

Shortly after discovering Johnson’s body 20 miles north of the capital, Saudi police swooped down on the al-Malz neighborhood in central Riyadh and exchanged fire with al-Qaida suspects.

Saudi officials in Washington said on condition of anonymity that five Saudi security officers were killed in the gunbattle. Two suspects escaped, said one Saudi security official who took part in the raid.

A U.S. official, who spoke on condition of anonymity, confirmed that al-Moqrin, 31, was one of the dead. A Saudi official said forensic tests would be conducted on the body to confirm his identity.

Saudi security officials say al-Moqrin trained with Saudi exile Osama bin Laden in Afghanistan and later fought in Bosnia and Algeria. Known as a smart and brutal tactician, al-Moqrin became the most-wanted militant in Saudi Arabia. A senior Saudi official in Washington identified the other militants killed Friday as:

l Turki al-Sahaid, said to have been involved in the May 29 shooting and hostage-taking attack on the oil hub of Khobar that killed 22 people, most of them foreigners;

• Faisal Abdulrahman Abdullah al-Dakheel, on the government’s list of 26 most-wanted militants;
• Rakan al-Sakhain, the second most-wanted man and an alleged associate of the mastermind of the bombing of the USS Cole in Yemen’s port of Aden in October 2000;
• and Ibrahim al-Drhaim.

Westerners targeted

Johnson is the second American to be kidnapped and beheaded in the Middle East in just over a month.

American businessman Nicholas Berg was beheaded by his captors in Iraq, and his last moments later appeared on a videotape posted on an al-Qaida-linked Web site. His body was found May 8. U.S. officials say al-Qaida-linked Muslim militant Abu Musab al-Zarqawi may have been Berg’s killer.

Johnson was seized on June 12, the same day that Islamic militants shot and killed Kenneth Scroggs of Laconia, N.H., in his garage in Riyadh.

Scroggs worked for Advanced Electronics Co., a Saudi firm whose Web site lists Lockheed Martin among its customers. The office number on Johnson’s business card was for Advanced Electronics.

The same week as Scroggs’ death, militants shot and killed another American, Robert Jacobs, and an Irish citizen in Riyadh.

It appears that Jacobs was also decapitated after being shot to death. Video shows his attackers bent over his body, making a sawing motion near the head, though there was no confirmation.