Columbine is on lockout, and it's not alone. Over 20 other schools in Jefferson County, Colo., also restricted access Tuesday as officials investigated what they called a "credible threat," the Denver Post reports. The FBI is leading the probe with help from the county sheriff and area police forces. "We too are taking this threat seriously," Aurora police tweeted. "...we are increasing police presence at our schools." Law enforcement requested the lockout after a "suspicious person" was seen in the area, says a rep for JeffCo Public schools. The move comes four days before the 20th anniversary of the Columbine High School shootings, which left 12 students and one teacher dead on April 20, 1999.
A lockout—which restricts school access and forces students to stay inside—is less dire than a lockdown, which is designed to protect students from a threat inside the school. But Colorado schools are also seeing more lockdowns as students report more possible threats in the age of mass shootings: "It's become as routine as fire drills," a Denver Public Schools offical tells the Post. "We don’t have many students that have started their academic career with us who aren't used to lockdowns." For more on the wider story, see the AP's report on survivors of Columbine or the New York Times' on what we've learned since the shooting. JeffCo Public schools will be hosting Columbine remembrance events from Thursday through Saturday, per KGUN9. (Read more school shooting stories.)