DENVER (AP) — Fears about student safety disrupted several Denver area schools Friday in the midst of events marking the 20th anniversary of the Columbine school shooting.

Students were kept late at a middle school in Lakewood so police could search the building after a tip was received about a possible weapon in the building. The lockout was lifted by late afternoon and school officials said no weapon had been found.

Another tip led to an evacuation of Brighton High School and tightened security at elementary and middle schools in the city north of Denver.

Tracy Rudnick, a spokeswoman for the...