Two custodians were found shot to death Monday inside a Chicago elementary school after one of them allegedly killed his co-worker before turning the weapon on himself, according to reports.A 48-year-old woman and a 63-year-old man were found unresponsive inside Mark Twain Elementary School just after 3:30 p.m., the Chicago Police Department said.Both were shot once in the head, authorities said. They were taken to local hospitals, where they were pronounced dead.TWO FOUND SHOT TO DEATH INSIDE CAR ON UNIVERSITY OF CHICAGO CAMPUS: REPORTAn unspecified weapon was found at the scene.School principal Matthew Moline confirmed the deaths in a letter to parents, WTTW-TV reported. He said shots were fired inside the building at a time when no students were present."I am sorry to share that members of our school community were impacted," he wrote.SEIU Local 73, the union that represents Chicago Public Schools custodial employees, confirmed both unidentified victims worked at the elementary school.DISPATCH AUDIO RELEASED IN MICHIGAN FAMILY MURDER-SUICIDE AS TROUBLED FAMILY'S SECRETS EMERGE"The only facts we know right now are that two families have lost a loved one and our prayers are with their families, and the staff, students, and families at Mark Twain Elementary School," SEIU Local 73 Executive Vice President Trumaine Reeves said in a statement.The older custodian was upset that he was slated to be transferred from the school, the Chicago Sun-Times reported, citing a police report. He allegedly shot his co-worker before shooting himself, according to the newspaper."We know that this news will be deeply concerning to our families and staff," Moline wrote in his letter. "We will work to provide additional information to the school community as the investigation proceeds."Fox News Digital has reached out to the police department, Chicago Public Schools, and Moline, the school principal.