A worker passes a derailed car from an Amtrak train that derailed Saturday near Nodaway, Iowa.

WASHINGTON -- Amtrak's westbound California Zephyr train derailed on Sunday in Iowa at a point where a length of rail had been installed as a temporary patch for a track defect, sources close to the investigation said yesterday, according to the Washington Post.

One passenger was killed in the derailment and 96 were injured. Further tests are needed to determine whether the temporary replacement rail also had a defect, but investigators are looking closely at the possibility, the sources said.

Crews for the Burlington Northern Santa Fe Railroad, which owns the track, intended to replace the temporary rail with newer rail in the next three weeks, the sources said.

The train usually would have been traveling at the 79-mph speed limit in that stretch of track. However, the horn on the nearly new lead locomotive was defective, and the train was forced to slow down through every grade crossing, with the assistant engineer getting out off the train and standing roadside to alert traffic. The train was still accelerating away from one of those crossings at the time of the wreck, and derailed at 52 mph.

The train began its trip in Chicago and was headed to Emeryville, Calif., across the bay from San Francisco. It had 195 passengers and 15 crew members when it derailed on a long straight stretch of track at Nodaway, Iowa, just east of Omaha.

Of the 96 people who were injured, seven remained in hospitals yesterday, one of them in serious condition. Sources said the soggy ground in the area of the wreck cushioned the impact as cars left the track and helped lessen the severity of injuries.

The Associated Press said relatives had identified the dead passenger as Stella Riehl, 69, of Widefield, Colo., who was returning home with the ashes of her brother, who died last week in Des Moines. Sources said the container with the ashes was located in the wreckage yesterday.

The National Transportation Safety Board was investigating the accident, but was characteristically cautious about whether broken rail found in the wreck had been part of the cause or had broken under the impact of the derailing train.

"Something appears to have been wrong back in the train between the interface of the wheels and the rail -- something we still haven't determined . . ." said Ted Turpin, the safety board's investigator-in-charge.

However, other sources pointed out that a computerized detector car, which checks the track monthly for hidden defects, had located such a defect in the last few weeks. Following standard policy, BNSF crews were dispatched to cut a long gap in the rail, which is welded into lengths of at least a quarter-mile on almost all main line railroads. Another rail about four yards long was bolted into the gap.

The railroad had intended to replace the welded rail in the next few weeks. No detector car had passed over the temporary rail since it was installed.

While modern rail may look much like the rail of 50 years ago, it is manufactured using special processes to avoid defects. Detector cars owned by the railroad or private companies patrol rail lines using ultrasound or other processes to locate defects before they become serious.