Authorities say an 11-month-old girl has died after being locked inside a car for 15 or 16 hours in suburban St. Louis.

The St. Louis Post-Dispatch reports that the Florissant Valley Fire Protection District received a call around 4:30 p.m. Sunday about an infant who wasn’t breathing and found the child unresponsive in Calverton Park. First responders were unable to revive her.

It’s unclear why the child was left inside the car for so long. The high temperature in St. Louis on Sunday was 79 degrees (26.11 Celsius). Police have questioned two persons of interest in the girl’s death.