DALLAS (AP) - A school in a wealthy Dallas enclave has canceled classes after a box of .22-caliber bullets was found in a bathroom in the second apparent threat in as many days.

Officials with Highland Park High School say police are investigating who left the shells Wednesday morning in a boys' restroom. The school went into lockdown and then classes were called off Wednesday afternoon.

University Park police Capt. Leon Holman says a threatening note was found Tuesday morning at the school but in a different bathroom. That hoax also forced classes to let out early for the day.

The school in January received three other hoax notes. Holman says all four notes were discovered in the same restroom.

(Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.)