Flags were flying at half-staff over the Colorado Capitol and other government buildings Monday, the 10th anniversary of the Columbine High School shooting massacre.
State lawmakers planned to pass a resolution titled "Triumph Over Tragedy" to mark the occasion.
But plans for Gov. Bill Ritter to address the Legislature in the state House of Representatives chamber were canceled at the last minute because the governor didn't have the required permission of House Speaker Terrance Carroll.
"Traditionally, the governor doesn't come on the floor unless it's the State of the State speech, and I'm not inclined to change that precedent," said Carroll. Both Carroll and Ritter are Democrats.
A memorial service was planned for Monday night in Clement Park, which is next to the school in the south Denver suburbs, and a "lie-in" in support of gun control is planned at the Capitol.
On the morning of April 20, 1999, two Columbine seniors unleashed an attack with guns and pipe bombs killing 12 students and a teacher. A bigger bomb, which they hoped would destroy the crowded cafeteria, failed to go off.
The gunmen, Eric Harris, 18, and Dylan Klebold, 17, committed suicide.
On the anniversary, Oprah Winfrey canceled an episode schedule to air Monday, "10 Years Later: The Truth about Columbine."
Winfrey posted a message Monday morning on her Facebook page, saying that after she reviewed the taped show, she decided to pull it because of its focus on the two gunmen. She urged viewers to keep the Columbine community in their thoughts.