ESCONDIDO - Three teenage boys were killed and a fourth was seriously injured Wednesday afternoon when their car crashed as they sped down Interstate 15 toward a high school graduation celebration in San Diego, authorities said.

The crash occurred at 2 p.m., when the victims' 1993 Acura Integra flipped over and struck a tree on the side of southbound Interstate 15 immediately north of the ramp to Highway 78, California Highway Patrol officer Tom Kerns said. The impact shot the car some 20 feet off the roadway, and authorities closed one lane of the freeway to investigate, causing traffic backup for several hours.

The Integra's occupants - all Perris High School students - were believed to have been racing with a black Honda or Acura that passed the Integra and sped off to the south after the collision, Kerns said. Both vehicles were traveling between 90 and 100 mph, he said.

Authorities were still seeking the second driver Wednesday night.

"It was not a hit-and-run, but maybe (the black vehicle) had something to do with why (the Integra) collided," Kerns said. "Possibly the black vehicle caused this vehicle to get out of control."

Alcohol was also considered a factor, and officers found multiple large, unopened cases of beer, as well as about a half-dozen opened and unopened beer cans, strewn around the crash site, the officer said. Witnesses also spotted the teens waving beer cans out of their windows as they passed school buses filled with fellow students headed to the graduation event, he said.

The collision crushed the Integra beyond recognition, killing Pablo "Paul" Ruiz, 18; Javier Aguayo, 17; and Anthony Oneil, 17. Two of the four were thrown from the vehicle, including 18-year-old Jose Espinosa, who survived. Espinosa was taken by ambulance to Palomar Medical Center in Escondido, Kerns said.

Espinosa underwent surgery and remained in critical condition, hospital spokesman Andy Hoang said just after 9 p.m.

The black vehicle that had been racing the Integra was further described as having black rims and tinted windows. It was unclear if that car contained other students or if it was an unrelated vehicle that started racing with the teenagers, but Kerns said the occupants of the two vehicles had been motioning to each other as they raced.

"According to witnesses, the two vehicles were in communication with each other, motioning, possibly flipping each other off," the officer said. "We don't know whether it was a play thing or on purpose."

The victims' Integra had a custom modified manifold, which connects to the engine, but it did not have any high-end racing modifications, he added.

Leslie Ventuleth, spokeswoman for the Perris Union High School District, said the victims - all seniors - had opted not to take school buses down to a school-sponsored senior beach party at Mission Bay, and were driving their own vehicles when the crash occurred.

About 80 students were scheduled to attend the event, and most left in the school's two buses, which turned around and returned to the campus when authorities heard news of the crash, Ventuleth said.

Another two cars containing fellow students that were friends of the victims were also traveling behind them and were not racing, Kerns said.

The drivers of those vehicles pulled over after the crash. A short time later, some teens sat on the side of the freeway, staring teary-eyed at the roadway as others spoke with officers.

Three young men leaving the site of the crash in the late afternoon remained visibly shaken, wiping tears from their eyes as they walked. They declined to be interviewed.

Kerns credits high school programs such as "Every 15 Minutes" and sober graduation with an overall decrease in graduation-time crashes involving high school students.

Still, "it is a common occurrence. It's a rite of passage in the wrong direction," he said. "There is a prolific abuse of alcohol … they're taking huge risks."

Perris High School's graduation is scheduled for Saturday, and graduation practice was held Wednesday morning, Ventuleth said.

Counseling staff was available to students Wednesday and will be again Thursday, she said. A memorial service is scheduled to take place on campus this week and the graduation ceremony is to proceed as planned.

- Staff writers Ann Moss, Jo Moreland and Yvette Urrea contributed to this report. Contact staff writer Sarah Wilkins at (760) 761-4414 or swilkins@nctimes.com.