CHICAGO – The former setting of a medical mystery is now a pile of rubble. But for Gayle Palmer, the final chapter has yet to be written.

In recent weeks, BP demolished Building 503 of its Naperville, Ill., research campus where at least six former chemical researchers of what was then Amoco Corp. — including Palmer’s husband, David Palmer — developed a deadly form of brain cancer in the 1980s and 1990s.

Researchers who conducted a three-year study of the cancer cluster concluded those six cases of glioma probably were workplace-related. Yet the scientists never could identify the source of the workers’ ailments.

The demolition of Building 503 gave little solace to Palmer and other victims’ relatives who still have questions.

“We still don’t know what happened,” Gayle Palmer said. “If we had a definitive idea of the source it might have brought closure, but we never did get that.”

Once, the 39 labs and offices on the third floor of Building 503 were a beehive of researchers looking for new chemical products and polymers. But after an alarming number of employees at the Naperville research campus were diagnosed with brain tumors, Amoco appointed university researchers to look into the matter.

The six employees who died of cancer all were long-term chemical researchers working in Building 503. Five of the six men worked on the third floor, which was later evacuated. At least 13 other tumors, all benign, showed no pattern that suggested a link to the job, the researchers said.

At least two dozen other lawsuits were filed on behalf of employees who contracted other types of cancer after working for Amoco at the Naperville facility.

BP divested its chemical business in 2005.