SALT LAKE CITY -- Federal investigators have launched a broad probe of a bus crash that killed nine Arizona skiers in southeastern Utah, from the driver's background to road conditions and the vehicle's equipment, an official said Wednesday

Pete Kotowski, who is leading the investigation at the National Transportation Safety Board, described the process so far as "fact finding."

"We're gathering evidence, information here at the site, taking statements from persons involved," Kotowski said.

A charter bus carrying 51 people to Phoenix after a long weekend at a Colorado ski resort careened off a remote two-lane highway and rolled down an embankment Sunday night. The roof was sheared off and most passengers ejected from the bus.

Four people were in critical condition at hospitals in Colorado and Utah.

Kotowski said authorities recovered a data recorder from the bus, commonly called a "black box."

"Whether it's been damaged to prohibit us from getting any information is unknown," he said.

The bus' electronic engine controls could yield information about speed and any "hard stops" before the vehicle lost traction, Kotowski said. Initial findings could be revealed next week.

Investigators have gathered at a garage about 130 miles north in Green River, where they are examining the wreckage.

Kotowski, speaking to reporters on a conference call, didn't reveal much about what his team had learned three days after the crash.

He said the bus was part of a 17-bus caravan that departed Telluride, Colo. It went off Highway 163 near Mexican Hat about 7:30 p.m. MST in the Four Corners area, where Utah meets Colorado, New Mexico and Arizona.

A second bus discovered the wreck about 20 minutes later, Kotowski said.

Friends Defend Bus Driver

Friends are defending the driver of a tour bus that crashed Sunday night in Utah, killing nine Arizonans.

Those who knew Welland Lotan, 71, told CBS 5 News they have nothing but good things to say about him.

Lotan has been staying in the Weavers Needle Travel Trailer Resort in Apache Junction. His friends say he's recovering from injuries he received in a Flagstaff hospital.

"We're concerned but we don't know much about it," said one resident.

The Utah Highway Patrol said it is checking into statements that Lotan was text messaging during the trip.

Menawhile, the National Transportation Safety Board is looking into Lotan's background and medical history, as well as his qualifications and experience.

The NTSB said as long as a driver meets specific criteria and skills and is medically certified, age is not relevant.

Lotan said he was "just doing the speed limit" of 65 mph when he failed to negotiate a turn that led to the crash, an Utah investigator said.

A Utah Highway Patrol sergeant says "weather absolutely was not a factor."

Eight of the people killed in the accident were from the Phoenix area, including four high school students and a 7th-grader. The ninth victim was from Tucson. Some 20 other people were hurt.

Investigators said they found a data recorder and video equipment inside the mangled wreckage.

The devices may help determine why the bus, returning to Phoenix from a ski trip to Telluride, Colorado, left the road and rolled down an embankment.