2 custodians found shot dead inside Chicago elementary school, police say

Both people were found with gunshot wounds to the head, police said.

Two school custodians were found shot dead on Monday inside Mark Twain Elementary School, just north of Chicago's Midway International Airport, according to ABC News' Chicago station WLS.

The Chicago Police Department said in a statement that two adults were discovered unresponsive on Monday afternoon -- one 48-year-old female victim with a single gunshot wound to her head, and 63-year-old male also with a single gunshot wound to the head.

Both people were transported to Christ Hospital in critical condition and pronounced dead at the hospital, police said.

A weapon was recovered on scene, the statement added. The investigation is ongoing, police said.

The school's principal said that no students were inside the building at the time of the shooting, WLS reported.

ABC News' Darren Reynolds contributed to this report.