Thursday, April 22, 1999 Published at 13:38 GMT 14:38 UK
Killers' parents pray for victims
Tributes to the shooting victims are left in a snowy park by the school
The parents of the Colorado school killers have expressed their "heartfelt sympathy" to the victims of the massacre and their families.
"Our thoughts, prayers and heartfelt apologies go out to the victims, their families, friends, and the entire community," the Klebold family said.
Harris' parents said: "We want to express our heartfelt sympathy to the families of all the victims and to all the community for this senseless tragedy."
Detectives have begun examining the Internet site believed to have been be used by the two students. The site is being dismantled by the service provider, America Online.
As the investigation continued, memorial services were held across the city, and counsellors offered support to those touched by the tragedy.
Harris and Klebold rampaged through Columbine High School with guns and bombs, killing 12 students and one teacher before turning the guns on themselves.
(Click here for a map showing the school layout)
The pair, who reportedly belonged to school clique called the Trenchcoat Mafia, wore long black coats and masks and laughed repeatedly as they targeted their victims.
'Could not have worked alone'
Sheriff John Stone said they found so many home-made bombs that he doubted that just two people could have carried them into the school.
More than 30 devices were found, including pipe bombs, timed explosives and improvised hand grenades.
One bomb was rigged to the petrol tank of a car in the school car park.
The county's prosecutor, Dave Thomas, said: "There is some belief that there are other people at least knowledgeable about this."
Three people, believed to be friends of the suspects, were arrested in a field near the school and led away in handcuffs.
A police spokeswoman said they were wanted for questioning and were not thought to be directly responsible for the shootings.
Shrine for the dead
Throughout Wednesday, pupils wearing blue and silver ribbons, the colours of Columbine High School, returned in tears and clung on to each other as they laid flowers at two shrines.
It was the worst massacre in a string of school shootings that have rocked US communities in recent years.
Calls for gun control
The shootings have once again prompted calls for tighter gun control.
US President Bill Clinton used a speech to White House volunteers on Wednesday to express national shock at the tragedy.
"We have to take this moment once again to hammer home to all the children of America that violence is wrong, and to show children by the power of our own example how to resolve conflicts peacefully," he said
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