Police: Teen who killed four in US school 'absolutely cold-hearted'

The 15-year-old American boy who used a semi-automatic pistol bought during Black Friday sales to shoot his classmates at point-blank range was "absolutely cold-hearted" and went to school with "the intent to kill people," the local sheriff said Wednesday.

Police said that on the night before the attack at Oxford High School in Michigan, second-year student Ethan Crumbley recorded a video on his cell phone saying he was planning to launch an attack at the school the next day.

The video was not posted online and there was no advance warning, according to Oakland County Sheriff Michael Bouchard.

"It's clear that he came out with the intent to kill people. He was shooting people at close range, oftentimes towards the head or chest," said Bouchard.

Four students, aged 14 to 17, were killed, and six other students and one teacher were wounded in the shooting. Two of the injured remained in serious condition in area hospitals Wednesday, while several others had been discharged.

At an arraignment in Pontiac, Michigan, Crumbley sat mute, masked and suited in a heavy protective vest, while attorneys and his parents joined in by video conference.

The teen was charged as an adult with state murder and terror charges, prosecutors said, because the crimes are "serious" and the attack was premeditated.

Crumbley's lawyer entered a "not guilty" plea.