PERRIS, Calif. -- A Riverside County teenager who was thrown from a car that crashed while speeding to a pregraduation beach party in San Diego has died, bringing the death toll to four.

An investigator with the San Diego County medical examiner's office said 18-year-old Jose Espinosa died at a hospital Thursday afternoon where he had been taken about 24 hours earlier.

Espinosa was admitted to the hospital with a fractured spine after the crash on Interstate 15 in Escondido that killed three other Perris High School teens.

Meanwhile, a corner of campus has turned into a shrine with candles and flowers and photographs of the victims. Grief counselors are on hand to help students and faculty.

A memorial service is planned Friday for the dead teens.

The state Department of Alcoholic Beverage Control was trying to determine Thursday who provided beer to the Perris High School students killed in a freeway crash in Escondido while on their way to a graduation week beach party.

"We're certainly looking ... to see if we can find out where the alcohol came from," said John Carr, information officer for ABC. "We're trying to find the source."

Javier Aguayo, 17, Anthony Oneil, 17, and Pablo "Paul" Ruiz, 18, all of Perris, died about 2 p.m. Wendesday on southbound Interstate 15 at state Route 78 as they headed to a school-sanctioned graduation week outing at Mission Bay's Belmont Park, according to the CHP and the San Diego County Medical Examiner's Office.

Investigators found beer cans at the crash scene.

The two 18-year-olds, who had been sitting in the back seat, were ejected and probably were not wearing seat belts, authorities said.

The 17-year-olds were both in front, said CHP Officer Tom Kerns.

The Acura Integra skidded off the freeway just north of Centre City Parkway in Escondido, according to the CHP.

The teens chose to drive to San Diego in a car, rather than take the buses provided for the seniors, said Perris High School Principal Penny Graham.

Alcohol, excessive speed and reckless driving may have been factors in the tragedy, according to authorities.

"It's very tragic, yes, but they also had a choice of where their lives were going," Kerns said. "It really didn't need to happen."

A witness reported that a motorist in a late-model, customized black car with tinted windows, possibly an Acura or Honda, may have been racing the driver of the Integra or cut him off.

Investigators want to talk to the driver of the car, which has black rims, tinted windows, a modified exhaust pipe and damage to its back end, Kerns said.

They asked that anyone with information on the whereabouts of the car and driver call the California Highway Patrol.

The teens were scheduled to graduate with their class Saturday.

"It rips your heart," said Carr. "These cases are very very difficult."

Carr said if investigators determine who provided the alcohol, the case will be forwarded to the district attorney's office for prosecution.

The Belmont Park event was among a series of planned graduation week activities, culminating with "Grad Nite" at Disneyland Thursday and Friday.

Kerns said the boys departed from campus at the same time as two school buses filled with classmates.

Graham said many of her students learned the names of the victims Thursday.

"It's very difficult right now, but the students are handling the news as well as can be expected," she said.

A memorial service for the students is set for 6 p.m. Friday on the campus at 175 E. Nuevo Road, Graham said.