Fort Lewis College police responded to a report of two unresponsive women in a parked car on campus late Oct. 11. The next day college President Tom Stritikus sent a letter to students informing them that one of the students had died and the other was in critical condition at the hospital.

No information was released about the women by the college but Stritikus said in his letter that campus police, who are in charge of the investigation, “indicated that a toxic substance was likely involved.”

The Durango Herald has since learned that the women were sisters and that the 18-year-old who was in critical condition died sometime within a week and a half after being admitted.

La Plata County Coroner Jann Smith, who originally reported no outward signs for a cause of death for the 19-year-old woman, confirmed Monday that recent results from toxicology reports shows conclusively that the women had no drugs in their systems besides marijuana.

Neither Smith nor investigators she spoke with have ever heard of anyone overdosing from marijuana, she said.

“It may have been carbon monoxide,” she said. “We just don’t know yet.”

Campus police have released no information about the investigation. Smith has refused to release the names of the sisters.