TAMAROA, Ill. -- Federal investigators are focusing on a joint in the railroad tracks as the possible cause of a train derailment here that forced the evacuation of nearly 1,000 Southern Illinois residents for several days.

"We do have information that the rail broke under the train," said Ron Hynes, an investigator at the National Transportation Safety Board's laboratory in Washington, where technicians are examining wreckage from the derailment.

A 21-car Canadian National-Illinois Central freight train carrying hazardous and flammable chemicals derailed while passing through the center of Tamaroa on Feb. 9.

The train was carrying methanol, vinyl chloride, hydrochloric acid and formaldehyde, each either flammable or potentially toxic. Some chemicals spilled from ruptured train cars, causing the evacuation of everyone in and around this town of 800, with those who live closest to the wreck out of their homes for almost a week.

No one was injured.

Examiners began to focus on an insulated rail joint after a railroad worker found a piece of broken rail at the accident scene. The joint had been installed on Jan. 23, less than three weeks before the train derailed, around the spot where the cars first left the tracks.

Could be summer

Definitive answers won't come soon, Hynes said. It could be summer before investigators know for sure why the train left the tracks, he said.

Tamaroa is 28 miles north of Carbondale along U.S. 51.

The Canadian National Railway Co. has paid about $400,000 in settlements from the derailment, said company spokesman Jack Burke. The money has gone to about 90 percent of residents and local business owners eligible for payments, he said.

Burke declined to comment on the NTSB investigation.

The railroad is working with the Illinois Environmental Protection Agency on a long-term soil monitoring program at the derailment site, Burke said.

During the long cleanup, officials said repeatedly that air, soil and water around the site had not been contaminated.