A fiery crash involving a City of Three Forks (Mont.) fire truck and pickup truck that killed six including the city's fire chief was the result of a mechanical failure, investigators said.

A nearly two-month investigation by the Montana Highway Patrol concluded that the 2002 International fire engine's front drivetrain caused Chief Todd Rummel to lose control of the vehicle on June 19. The truck struck a 1997 Chevrolet pickup truck carrying a family of five in a head-on crash on U.S. Highway 12.

The collision caused a puncture in the fire engine's diesel fuel tank, spraying fuel and engulfing both vehicles in flames, reports the Associated Press.