LITTLETON, Colo. (AP) — Columbine High School is moving ahead with ceremonies marking the 20th anniversary of an attack that killed 13 people, and the community is awaiting more details on what led a teenager allegedly obsessed with the 1999 shooting to buy a shotgun and kill herself in the snowy foothills nearby.

A religious service Thursday night kicked off three days of commemorative events leading to a day of community service projects and a ceremony Saturday at a park near the school.

An already tense time at the school was exacerbated after 18-year-old Sol Pais traveled to Denver from Miami on Monday and immediately bought a pump-action shotgun.

Her body was found Wednesday, about 24 hours after Columbine and other schools locked their doors in response to fears that she intended to carry out her own attack.