MONTROSE, Colo. -- A 17-year-old female student at Montrose High School was seriously injured in an attack Tuesday, and students were sent home after a suspect ran from the school and was arrested.

The victim of the attack was identified by the Montrose Daily Press as sophomore Mallory Haulman, the daughter of Denny Haulman, the production manager at the newspaper.

Montrose Police Chief Tom Chinn said the girl was slashed with a straight-edged weapon by another teenager at about 8 a.m.. The girl was walking down the crowded main hallway with her sister, before classes started for the day, when she was attacked, police said.

A student interviewed by the Denver Post said she witnessed the attack.

"He calmly walks up to her and grabbed her by the throat," Paola Gomez told the Post. "He pulled her head back and slit her throat."

Gomez told the Post that the injured girl dropped began screaming, "Oh, my God. Someone help me."

She told the paper that the suspect then turned around and looked straight into Gomez' eyes "as if nothing happened and calmly walked out of the building."

A police officer spotted the slashing suspect near the school and ran after him, police said. He was cornered a short distance away and placed under arrest. Police said he was not a student at the school, but wouldn't say how old he is.

Police have not said if they recovered the weapon used.

A motive for the attack was not immediately clear and it wasn't known if the attacker knew the victim. The school is reviewing its surveillance video.

Superintendent George Voorhis said that the teenaged suspect had been in other educational "placements," including an alternative school in Montrose and a school in Grand Junction, according to the Montrose Daily Press.

"The kid came in off the street. ... Now we want to go back and ask, 'Could we have been more proactive?' We don't think we can," Voorhis told the Montrose Press.

Haulman was rushed into surgery at Montrose Memorial Hospital where her mother, Alicia, works as a nurse in the intensive care unit. She was listed in serious condition after surgery.

After the attack the school was immediately placed on lockdown and Principal Jill Myers dismissed classes for the rest of the day. The school will make counselors available for students when they return to class on Wednesday.

An informational meeting was held Tuesday night in the Lloyd McMillan Gym.

"This will be a time for parents to come together to learn more about today's incident," said Myers.

Classes will resume on Wednesday.

Montrose is 285 miles southwest of Denver.

For more on the story, read the Montrose Daily Press coverage.