DARMSTADT, Germany (AP) -- Prosecutors asked for murder charges Tuesday against three U.S. teenagers accused of tossing rocks from a highway bridge at passing cars, killing two drivers and injuring five other people.

The three teenagers, the children of U.S. military personnel, were arrested Monday night by German and U.S. military police at the U.S. Army's Lincoln housing area near Darmstadt, just south of Frankfurt.Darmstadt police spokesman Heiner Jerofsky said all three -- ages 14, 17 and 18 -- confessed during questioning overnight to having thrown large stones late Sunday from a nearby pedestrian bridge at cars on the four-lane highway underneath.

In a statement Tuesday, Jerofsky said the group had been "meeting regularly" for the past four to six weeks to throw rocks at moving and parked cars. "There's still no clear picture at the moment about the actual motive," he said.

Prosecutors asked a magistrate court for a warrant charging the three suspects with murder and attempted murder. A ruling was expected within 24 hours, and approval was expected, Darmstadt chief prosecutor Georg Balss said.

The three, who have lived in Germany at least a year and a half, were to be tried under the German justice system, Balss said. They were being held in investigative custody, and their names were withheld.

A juvenile murder conviction carries a sentence of up to 10 years.

Prosecutors had not yet decided whether to try the 18-year-old as an adult.

In a statement issued by the U.S. Embassy in Berlin, Secretary of Defense William Cohen said he was "shocked and saddened" by the "tragic accident" and pledged continued close cooperation in the investigation.

The narrow bridge from which the three teens allegedly tossed the rocks links the U.S. military housing to an American school. Police suspect the stones were taken from a nearby construction site.

A 20-year-old Darmstadt woman was killed Sunday night when a handball-sized rock smashed through her windshield while she was driving on the B3 highway. Her grandparents, both 75, were injured -- the grandmother seriously, police said.

A short time later, a 41-year-old woman from nearby Pfungstadt was killed when a rock splintered her windshield from the same bridge.

In all, six cars were hit by stones thrown from the bridge over a period of about 15 minutes, police said. Three other people in the other cars received minor injuries.

A 15-year-old arrested with the other teens knew about the stone-throwing, but he was not involved and was released after questioning, Jerofsky said.