ST. LOUIS (AP) — Authorities say a 1-year-old boy who died after police responded to a report of a child not breathing at a St. Louis day care may have been left inside a vehicle.

St. Louis County police said in a news release that officers responded around 6 p.m. Monday to the Casa Dia Montessori school. The child was rushed to a hospital, where he was pronounced dead.

The Montessori said in a statement that the boy was unresponsive in his mother’s van when she arrived there at the end of the day. The statement described the death as a “terrible accidental loss.” Police say the boy may have been left in a vehicle for “an extended period of time.”

An autopsy is planned for Tuesday. The boy’s name wasn’t immediately released.