LOS ANGELES (WCMH) — Federal investigators are looking into a disturbing case in Southern California in which a teacher is accused of contaminating students’ musical instruments with semen.

The flutes were decorated and painted by SoCal students through a program called “Flutes Across the World.” As many as 13 districts could be affected, according to a statement from the Los Angeles Unified School District.

NBC4 Los Angeles reports several school district alerted parents on Friday and asked them to turn in any flutes to authorities. The California Department of Justice and the United States Postal Service launched an investigation.

Investigators want to test all the flutes, as they believe they are contaminated with semen from the program’s teacher.

A parent named Nate told NBC4 Los Angeles that he went to police Friday to turn in his child’s flute.

The teacher has been arrested. His name has not been released.