ST. LOUIS (AP) _ A teen-ager waiting at a school bus stop with a pistol began firing after the bus doors swung open Thursday, killing a pregnant 15-year-old and wounding the driver before running away. The baby was in critical condition.

Dozens of police officers searched the city's north side for the gunman, who was believed to be 16 to 18. Police were unsure of a motive.

Police were also uncertain whether Kyunia Taylor, who was sitting in the first seat inside the door on her way to school, had been targeted or was shot at random.

The shooting took place shortly before 7 a.m. when the small bus carrying the driver and three students pulled up to its regular stop. When the door opened, the gunman asked if the bus was going to Beaumont High School. The driver said yes.

``He shot the bus driver and then began firing at the bus,'' police spokesman Tom Geiser said. ``We don't believe he actually ever got on the bus.''

The 60-year-old bus driver, Richard Lanemann, was in serious condition with three gunshot wounds.

Two bullets struck Taylor, a ninth-grader, in the chest. She was dead on arrival at the hospital.

Doctors delivered her baby by Caesarean section. The 3-pound girl appeared to be one to three months premature.

``The fact that the mom had been dead for a period of time meant that although the baby's heart may have continued to beat, there was no oxygen going to the baby or to the baby's brain,'' said Dr. Timothy Buchanan, who delivered the baby. ``The baby's outcome is in doubt.''

At the school, halls were mostly vacant Thursday morning. A crying girl was escorted to an office by two adults. Security was already tight _ all students must pass through a metal detector each day _ but it appeared that movement was also being restricted.

Principal Floyd Crues announced Taylor's death over the public address system. ``At the moment we have our counseling crisis management staff in place to deal with the students and staff,'' Crues said.

Taylor entered school there in September. Few people knew she was pregnant, Crues said.

The shooting happened in a high-crime area. Many of the brick two- and four-family apartment houses have iron bars over the windows. A home partially gutted by fire stands near the intersection where the shooting occurred.

Neighbors described Taylor as a quiet girl.

``She kept to herself,'' Darnell Shannon said. ``She didn't mess with nobody.''

Police Chief Ron Henderson said the investigation wouldn't stop at catching the gunman.

``Were going to really look at this and see what we can do to better protect'' students, he said. ``We are just not going to have folks attacking these school buses. We're just not going to have it.''