Officers stormed the school after more than three hours, at which point the lone gunman reportedly shot one of his two hostages and then himself.

The attacker, who appeared in a classroom just before noon (1800 GMT) on Wednesday, initially took six hostages, all of them girls, but gradually released four of them as he talked to police negotiators.

Other students and staff at Platte Canyon and a neighbouring middle school, which have nearly 800 pupils between them, were evacuated during the siege.

The town of Bailey is only a short drive from Columbine High School, where seven years ago two students killed 13 people before taking their own lives.

State records show he had criminal convictions for theft and marijuana possession dating back to 1973 and in July he was arrested for obstructing police in west Denver.

"We firmly believe, without a shadow of a doubt, that the suspect was responsible for the death of the child," said Joe Morales, executive director for the Colorado department of public safety.

Another student at the high school, Cassidy Grigg, went on US television channels NBC and ABC to give an account of how the gunman had chosen his hostages and threatened him personally.

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