Thomas Neal possessed images and videos of child pornography on his cell phone when he flew from O'Hare airport to Benito Juárez International Airport in Mexico City on June 17, the U.S. attorney's office said.
Upon arrival, Neal was selected for secondary screening by Mexican border authorities, and authorities saw images on Neal's phone that constituted child pornography, the release said.
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Mexican border authorities secured Neal's phone and other luggage, including two laptops and six electronic storage devices and put him and the luggage on a flight to George Bush Intercontinental Airport in Houston.
When Neal got to Texas, Homeland Security Investigations found observed hundreds of files that constitute child pornography, officials said.
The release said Neal is employed as a teacher at a high school.
Niles Township High School District 219 is consulting with legal counsel and cooperating fully with authorities during this active investigation, a spokesperson for the district said.
The employee under HSI investigation has been placed on suspension.
"D219 takes seriously any complaint or allegation against an employee, and we will continue to work with authorities to ensure appropriate actions are taken to keep our school community safe," the district said.
The charge of transportation of child pornography is punishable by a mandatory minimum sentence of five years in a federal prison and a maximum of 20 years.
Neal is currently detained in federal custody pending a detention hearing on Monday in Chicago.