LOS ANGELES (AP) — Investigators zeroed in on brakes as a possible cause of last weekend's deadly tour bus crash that killed seven people, including a 13-year-old boy from San Diego and his mother and grandmother.

Victor Cabrera-Garcia, Elvira Garcia Jimenez and Guadalupe Olivas were among 38 people on a daylong trip from Tijuana, Mexico, to see the snow in the San Bernardino Mountains. The bus crashed Sunday evening near Yucaipa as it made its way down meandering state Route 38.

Beginning a review that could take months, investigators from the California Highway Patrol and the National Transportation Safety Board started collecting evidence about the bus, road conditions, and possible driver error or fatigue that could have played a role in the crash.

A team of NTSB officials was dispatched Tuesday to the offices of bus operator Scapadas Magicas LLC, in National City, near San Diego, where they interviewed owners and employees and gathered documents on the vehicle's maintenance history.

The roadworthiness of the 1996 bus loomed as a key issue after the driver told investigators the brakes failed as it descended from the popular Big Bear ski area, and federal records pointed to a history of brake maintenance problems.

"We are going to look very closely at the brakes as we will every other mechanical system on the bus," NTSB spokesman Eric Weiss said.

The bus, its front roof collapsed and windows shattered, was towed to an auto yard in Ontario that the Highway Patrol uses to store evidence, Officer Mario Lopez said.

The CHP's criminal investigation, which is routine, is "to determine if there was any criminal action that caused this collision," Lopez added.

The bus careened out of control as it descended the mountain road, striking a sedan and flipping before slamming into an oncoming pickup truck hauling a trailer. The accident scene left even veteran investigators shaken, as debris and body parts littered the road. Dozens were injured and several remained in critical condition Tuesday.

Victor Cabrera-Garcia's aunt, Luz Garcia, told The Associated Press she believed the boy went to see the snow with his 40-year-old mother and 61-year-old grandmother as a late present for his Jan. 13 birthday.

"It's hard because we are suffering the pain from losing members from three generations," Garcia said, speaking in Spanish. "Each one hurts equally. It's horrible."

The boy was his mother's only son and they lived with his grandmother, Garcia said. He loved soccer and played on a local team as a goalie. One of his happiest moments, she said, was attending the championship game of Tijuana's "Los Xolos" soccer team in December when they won the First Division title.

Others killed in the crash were Tijuana residents Liliana Camerina Sanchez Sauceda, 24; Aleida Adriana Arce Hernandez, 38; Rubicelia Escobedo Flores, 34; and Mario Garcia Santoyo, 32, authorities said.

Investigators will attempt to determine if a mechanical failure, driver error or a combination of both caused the crash. It will encompass a broad range of factors, from road conditions to witness accounts, an exhaustive review of the vehicle to an evaluation of the driver and his decisions. Investigators have also taken a blood sample from the driver.

Just before the crash, the driver, Norberto B. Perez of San Ysidro, shouted to the passengers that the brakes had failed and urged them to call emergency services, passengers said.

"If it didn't have brakes or did have brakes, it would leave different types of evidence," said Bob Snook, an accident consultant who recently retired from CHP after working on accident investigations for 25 years.

The investigations are "basically car autopsies, because they will go over that bus with a fine-toothed comb," Snook said. Continued...