The Latest: Denver schools tighten security after threat

LITTLETON, Colo. (AP) — The Latest on a lockout at Columbine High School and other Denver area schools (all times local):
4:10 p.m.
All schools in the Denver area are being urged to tighten security after what appears to be a credible threat caused a lockout at Columbine High School and more than 20 other schools in the area.
Patricia Billinger, a spokeswoman for the Colorado Department of Public Safety, says the agency made the recommendation because Tuesday’s threat was deemed &ldq