DENVER -- A 15-year-old mentally challenged teenager shot by Denver police Saturday after he allegedly threatened his mother with a knife died at the hospital.

The teen -- who was identified as Paul Childs, a sophomore at East High School -- was hospitalized after the shooting and died about four hours later.

Police spokesman Detective John White said police were called to a home shortly after 1 p.m. after someone reported that a boy was allegedly threatening his mother with a knife.

White said the teen had a knife when police arrived and when he failed to respond to police demands to drop the knife, an officer shot him.

The officer and other witnesses were being interviewed.

The boy's mother told 7News that Childs was mentally disabled and that he probably didn't understand what was happening when police arrived at the house.

White said a police investigation into the shooting was underway, but indicated that the officers used potentially lethal force to protect themselves from a threat.

"A knife can inflict very serious injury and even death at short range," said White. "I believe there was a short distance between the officers and this young man at the time this (shooting) occurred."

At least one neighbor told 7News the teenager didn't seem to have a violent past.

"He was slow, but he was really nice," said neighbor Zalybia Scott. "He didn't bother anybody. I have never seen him be violent before."

It was not immediately known exactly how many times the victim was shot.