Images from the shooting at Perry Hall High School were released Monday. Robert Gladden will serve 35 years in prison.

TOWSON, Md. (WJZ) — Chilling confession. There’s new video of the teenage shooter who opened fire inside Perry Hall High School talking about how he planned the attack and why he did it. Robert Gladden, 15, was sentenced by a judge Monday.

Meghan McCorkell reviewed the tapes and has the frightening insight.

In those new interview tapes, Robert Gladden admits he’d been plotting the attack for months. Now a judge has sentenced him to 35 years behind bars.

Slideshow: Images From The Shooting

Surveillance images show Gladden pull a shotgun from his pants inside Perry Hall High School’s cafeteria. As he opened fire, teachers rushed in his direction, pinning the teen against a vending machine.

“The pants I had had really deep pockets so I put the stock in the pocket and put it under my shirt,” Gladden told detectives during just released interview tapes.

Gladden told police he warned two friends to leave the school before the attack. He then assembled the gun and walked into the cafeteria.

“I didn’t really have any one person I was trying to kill. I just turned to the side and shot,” he said.

WEB EXTRA: Unedited footage of Robert Gladden’s interview. These clips contain explicit language.

That shot hit 17-year-old Daniel Borowy, a special needs student.

Gladden brought 21 shells with him. If he hadn’t been stopped, he said his plan was to have “gotten to as many as I could and then gotten to kill myself.”

When a detective asked him, “So you wanted to kill as many people as you could in the school?” Gladden nodded his head yes.

In court, there were witness-impact statements.

“I see Robert with the shotgun and he points it at me. Zeroed in on me. He was looking at me dead in the eye. I have absolutely no doubt he would have killed me if others hadn’t stopped him,” said Kathleen Watkins, Perry Hall High administrator.

In court, Gladden’s father pleaded for mercy, saying he never saw this coming. His lawyer says the teen has issues.

“Now what we’re doing, we’re penalizing people with mental illness,” said defense attorney George Psoras Jr. “This act was insanity at its finest. Stupidity at its best. He’s crying out for heaven’s sake. He wanted to die that day,”

Daniel Borowy was hit in the back with a shotgun blast Aug. 27, the first day of classes at Perry Hall High School. Borowy, who has Down syndrome, missed more than two months of school while recuperating from his injuries.

His mother told the judge she now calls the school every single day to make sure her son is OK. He returned to school in November.

“I’ll probably be fearful for the rest of my life. But that’s just me,” said Rosemary Borowy. “My son is 17, but in his heart and mind, he’s like a 7-year-old. He was scared and confused. It was really hard for him. He went through a lot. I thought he was going to die. I’ve already buried one child and I didn’t want to bury another.”

“They’re hurting. We’re hurting. Everybody hurts. There’s no winner,” said Milton Borowy.

Gladden will be 50 years old when he gets out of prison.

During his sentencing hearing, Gladden read a statement apologizing to the Borowy family and asking for understanding.