An incident that closed down East Grand Rapids High School in mid August was part of what authorities said was "an elaborate riddle."

Authorities closed the high school Aug. 15 as a security precaution after suspicious packages were found on the campus.

Public safety officials said surveillance video showed three masked people breaking into the campus overnight carrying the packages. An investigation found the packages posed no security risk.

"Most significantly, the investigation revealed there was no intent to commit any violent or bomb threat type activity on the part of the three involved suspects," authorities said. "Their only goal was to create an elaborate riddle/scavenger hunt type adventure within the service tunnels beneath East Grand Rapids High School for their classmates."

Three 18-year-olds were charged with multiple offenses and charges are pending against a minor accused of larceny.