Mexican drug lord Joaquín Guzmán may have used a bird to test out the air quality of his escape tunnel before breaking out of prison.
According to Daily Mail, Mexican government officials found a dead sparrow in the trash can of Guzmán's cell after he escaped through a hatch in his shower area.
A small nest was also discovered in the cell's window, TIME reports.
Officials believe Guzmán had the bird fly through the tunnel to determine whether or not the pathway contained any harmful gases.
The New York Times reports coal miners use canaries for similar purposes.
After the sparrow's flight, the billionaire's accomplices allegedly traveled through the tunnel and met him at the hatch to return the bird that is now nicknamed "Chapito."
The Mexican newspaper Reforma revealed Guzmán left a small LCD television on in his cell to make guards at the maximum security prison think he didn't leave.
There are reportedly around 10,000 Mexican agents looking for Guzmán.
Yesterday, the surveillance footage from the cell, showing Guzmán walking back and forth several times before disappearing through a 20-inch hole, was released.
Citations: Did a little jailbirdie help El Chapo fly the coop Sparrow used to test escape route (Daily Mail), El Chapo May Have Used Bird to Test Escape Tunnel Air (The New York Times), El Chapo May Have Made His Escape With the Help of a Sparrow (TIME)