Once word spread that a bus carrying L.A.-area high school students was involved in a fiery crash in Northern California on Thursday night, dozens of parents and classmates frantically called and texted the teenagers, hoping their loved ones weren't among those killed.
On Friday afternoon, nearly 24 hours after the crash, parents and officials at some schools were still trying to track down missing children. As the hours passed, their fears worsened.
When Adrian Castro didn't show up to El Monte High School on Thursday, his best friend assumed he had decided to go on the trip to Humboldt State University. That night, Angel Gonzalez said, his phone buzzed with messages asking if Castro was OK.
"HMU bro!!" he tweeted to Castro, asking him to "hit me up" with news. The 19-year-old never responded. On Friday, he was identified by school officials as one of the students still unaccounted for.
Gonzalez, 18, said he was "just trying to process all this."
Ten people, including five students, were killed after a FedEx truck hit their bus head-on on Interstate 5 near Orland, Calif., officials said. The bus burst into flames, and more than 30 people aboard were injured.
Glenn County Sheriff Larry Jones said some of the victims were so badly burned it would take medical and dental records to positively identify them.
The bus was one of three caravaning to Humboldt State, including two from Union Station in downtown Los Angeles and a third from Fresno.
It was not immediately clear which Los Angeles-area students were on which bus.
Students on the two buses that left from Downtown L.A.'s Union Station were supposed to be divided into two groups: last names beginning with the letters A to L on one bus, M to Z on another, Humboldt State spokesman Frank Whitlatch said. But the teenagers "did what 17-year-olds do," and switched vehicles to sit with their friends.
Only one victim -- Arthur Arzola, a 26-year-old Humboldt advisor -- has been positively identified by coroner's officials. Relatives and school officials have identified a few of the others who have not been accounted for.
At Norte Vista High School in Riverside, a cloud hung over students preparing for prom night as they worried about the whereabouts of classmate Marisa Serrato, whose family told reporters she has been missing since the crash.
Marisa and her twin sister Marisol, both seniors, chose to skip the dance to visit Humboldt State University, said a classmate who gave only his first name, Elmer.
"We just don't know if they've found her," Elmer said.
Gabriel Sanchez, a spokesman for the Green Dot organization of charter schools, said officials believe students from two of its campuses -- Ánimo Inglewood Charter High School in Inglewood and Ánimo Jackie Robinson Charter High School in South Los Angeles -- were on the bus trip but they are still trying to confirm that and find out whether the teens are safe.
"We don't know for sure," he said, noting that some students may sign up for the trip but not actually take it. "We are still trying to find out the information."
L.A. schools Supt. John Deasy provided an updated list of 14 L.A. Unified campuses with students on the bus involved in the fatal crash. Deasy said he did not know if students from these schools were among the five killed.
"We're very worried about the condition of a number of students," he said in an interview, declining to elaborate further.
The bus was heading to Humboldt State for its "Preview Plus" program, which gives low-income and first-generation college students a free chance to visit the university. About 100 students typically attend the two-day session from the L.A. area, the university said.
Some students were invited but ultimately declined the invitation. Many schools spent Friday trying to determine if they had students on the trip.
Ten students from Alliance Luskin College-Ready Academy were accepted to Humboldt State and had been invited on the tour, but none decided to go on the trip, said Chalio Medrano, principal of the South Los Angeles charter.
"We've been in contact with families since last night clarifying and also in communication with college counselors and verified that all of our students were at school yesterday," Medrano said.
One of the students accepted, Monica Rivera, said she received several emails from Humboldt about attending the spring preview day, but the 17-year-old senior said she was too busy.
"I knew I wouldn't have time," Rivera said. "I was shocked thinking I could have been on that bus."
Investigators have launched and intensive examination of the crash, which was first reported about 5:40 p.m. Thursday.
California Highway Patrol Lt. Scott Fredrick said it remained unclear whether the FedEx driver – who officials said was among those killed – had fallen asleep, whether his semi had some type of mechanical failure or if there had been a collision with another vehicle in the moments before the bus was struck.
Fredrick said CHP investigators were being assisted by the National Transportation Safety Board, which sent a team that arrived at the remote Northern California scene Friday morning. Investigators would use "sophisticated surveying and mapping equipment," along with 3-D diagramming, to reconstruct what led up to the crash, he said.
Fredrick said investigators would also consider roadway and weather conditions. But he and others cautioned it could take up to six months for the CHP to complete its report.
"The investigation itself … is a long, tedious process," said Ruben Leal of the CHP. "We may not have some answers for months."
Carpenter said 31 people were transported to seven hospitals with injuries ranging from minor to critical. Nine people were pronounced dead at the scene, and another died later of severe burns.
More than a dozen agencies responded to the crash, which Jones said was heard up to a quarter-mile away. "This was a horrific collision," he said.
"The great irony here, the great sadness is these are the students California needs to be successful going forward," CSU Chancellor Timothy White said, saying the students "had their dream of going to Humboldt State taken away away by this tragic accident."
"The soul of the CSU has been cut deeply," he said.
Seven students from the doomed bus trip spent the night at the Veterans Memorial Hall in Orland, where they were being reunited with parents Friday. The Red Cross had set up cots, and volunteers brought water and food and blankets.
"Some students slept," said Scott Gruendl, a county health official. "Some students couldn't sleep."
On Friday morning, the high school across the street posted "Our thoughts are with you" on its sign. As the day wore on, a couple who lives nearby brought homemade cookies.
"There's nothing we can really do," said the baker, Juliana Gregory, who has four children of her own. "If we could, we'd give them a hug and tell them we're praying for them."