Despite warnings of impending terror acts, the homicide bombers in Riyadh (search) met little resistance when they attacked a housing complex that included Americans who have been training Saudi Arabian national guardsmen.

It was the second time in eight years that the Saudi business interests of Fairfax, Va.-based Vinnell Corp. (search) have come under terrorist attack.

On Monday night, it took the bombers 30 seconds to a minute to get through an iron gate, drive up to the building and detonate explosives, said a senior administration official on the plane of Secretary of State Colin Powell.

Seventy Americans employed by Vinnell lived in the building; seven of them died in the explosion and 15 others remain hospitalized with injuries, parent company Northrop Grumman said in a statement. Northrop Grumman (search) described the target as a residential and office facility. Two other company employees, both Filipinos, also died in the explosion. Details were not available on the death of an eighth American victim of the attacks.

After killing the sentries the bombers pushed the button that opened the iron gate to the compound.

"They had to know where the switches were," said the official, suggesting the terrorists had inside information.

A November 1995 car bomb blast destroyed a building in the Saudi capital that was headquarters for the U.S. Army training program in which Vinnell was deeply involved.

A former CIA officer suggested the warnings should have prompted stronger protection.

"Certainly there is vulnerability when it comes to homicide bombers, but nevertheless these are the people who are training the national guard, and the question is, `Why wasn't there better security?"' said Vincent Cannistraro, former counterterrorism operations chief at the CIA.

Northrop Grumman said in a statement that the company "took a number of measures -- in coordination with the SANG unit that provides security for the compound -- to heighten security of our operations and keep our employees aware of the threat."

The Saudi national guard protects the ruling monarchy and is the Saudi equivalent to the Republican Guard of Saddam Hussein, said John Pike, director of Globalsecurity.org, a defense policy group. Separate from the regular Saudi army, the guard is the descendant of the army that originally helped conquer the Saudi Arabian peninsula for the House of Saud, the ruling monarchy.

Saudi guards were protecting the complex at a time when there was a heightened state of alert for the country. The State Department announced May 1 that terrorist groups might be in the final phases of planning attacks against U.S. interests in Saudi Arabia.

Just a day before the deadly assault in the Saudi capital, an al-Qaida operative wrote in an e-mail to a London-based magazine that al-Qaida had set up "martyrdom" squads in Saudi Arabia to launch what he described as a "guerrilla war" on Saudi Arabia's leaders and the United States.

In the 1995 terror attack involving Vinnell, a car bombing that killed five Americans, Saudi Arabia obtained confessions from four Saudis and beheaded them before FBI agents were allowed to question them.

Vinnell was awarded its first training contract in Saudi Arabia, for $77 million, in 1975.

The work grew in size and scope over the years to the current multiyear effort worth more than $800 million to Vinnell and involving more than 1,000 employees plus almost 300 U.S. government personnel training the Royal Saudi Air Force, Saudi land forces and other elements of the Saudi military.

The training program, financed by the Saudi government and run by the U.S. Army Materiel Command, is one of numerous Pentagon efforts to make the Saudi air and land forces more capable of defending the oil-rich kingdom against Iraq or other potential enemies.

The projects were accelerated after the 1991 Persian Gulf War.

A subsidiary of defense giant Northrop Grumman, Vinnell advertises for ex-soldiers able to train the Saudis in battalion operations, the Bradley fighting vehicle, anti-tank weapons and physical security.

On its Web site, the company promotes itself as "a recognized leader in facilities operation and maintenance, military training, educational and vocational training and logistics support in the United States and overseas."

Vinnell also has operated eight Job Corps centers across the United States under contracts with the Labor Department.

The company took corrective steps when an audit in 2001 found $1.5 million in cost overruns by Vinnell at its Detroit Job Corps centers.

Founded in 1931, the firm began as a construction company that prospered in the construction of military bases during World War II and during the war in Vietnam.