CAMPBELLTON, Texas (AP) - Investigators say a broken drive shaft likely caused a Mexico-bound bus to veer off a south Texas highway before flipping -- killing two passengers.

The Department of Public Safety on Wednesday identified the two passengers who died as 62-year-old Christina Lozano Campos of Lewisville and 27-year-old Efrain Dominguez-Valenzuela of Brownsville.

The other 40 people on board also were hurt in yesterday's accident near Campbellton, about 45 miles south of San Antonio.

The Americanos USA bus went off Interstate 37.

A company official says the 15-year-old bus underwent its regularly scheduled maintenance the day before the crash. Details came from Bonnie Bastian with FirstGroup America, the parent company of Dallas-based Greyhound Lines. Americanos USA is operated by Greyhound.

Bastian says the regular inspection covered the engine, tires, brakes and wheels.