BOSTON -- Investigators are said to believe that catastrophic brake failure was the cause of Friday's fatal fire truck crash.

Firefighters: Kelley Was A Hero | Residents Describe Crash | Images: Fire Truck Crash

Firefighters riding in the truck said the driver was frantically pumping the brakes as the ladder truck hurtled down a steep hill, through an intersection, and into a high-rise apartment building, the Boston Globe reported Sunday.

"We're not stopping! We're not stopping!" the driver yelled, according to an unnamed source quoted by the newspaper.

Lt. Kevin Kelley, a 30-year veteran of the fire department, was killed instantly when the truck burst through an iron fence and slammed into the building. Kelley was riding in the passenger seat when the accident occurred.

The driver, firefighter Robert Bernard O'Neill, was released from Brigham & Women's Hospital Saturday. Two other firefighters, riding in the ladder truck, suffered minor injuries.

Boston Fire Commissioner Roderick Fraser has ordered an outside inspection of the brake systems on the city’s 44 fire trucks from the same manufacturer.

The truck that crashed had been serviced for brake problems in October, and was in the department’s repair shop several days ago.

Maintenance records also indicate that a faulty brake hose was fixed as part of $22,000 worth of repairs done to Ladder 26 on Oct. 14. Fraser called the work routine maintenance.

Boston police and Suffolk County prosecutors are conducting an investigation to rule out any criminal activity.

"Our investigation will be thorough, and the loss our city suffered Friday will remain foremost in our minds," Suffolk District Attorney Daniel F. Conley said. "Our thoughts and prayers are with Lieutenant Kelley's family, his loved ones, and his department."

Fraser said an additional investigation will be conducted by a Fire Department board of inquiry.

Kelley was a resident of Quincy and had been featured in a Discovery Channel documentary on Boston firefighters. He leaves a wife and three adult daughters.

A wake will be held for Kelley on Tuesday from 4 p.m. to 8 p.m. at Keohane Funeral Home, 785 Hancock St., in Quincy.

Kelley’s funeral will take place Wednesday at 10 a.m. at St. Ann Church, 757 Hancock St., in Quincy.