Updated 02/02/12 – 6:04 a.m.

CALUMET CITY, Ill. (CBS) — Police in Calumet City were defending their actions Wednesday after officers shot and killed a 15-year-old boy, who has a form of autism, after he threatened them with a knife.

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Stephon Watts’ family said he suffered from Asperger’s Syndrome — a high-functioning form of autism — and attention deficit disorder.

As CBS 2’s Susanna Song and WBBM Newsradio’s Steve Miller report, they claimed the boy was only holding a butter knife. Police would only describe it as a “kitchen knife.”

The deadly encounter happened at the boy’s home at 541 Forsythe Av. in Calumet City, police said.

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Calumet City Police Chief Edward Gilmore said the boy cut a police officer through his shirt sleeve with a “kitchen knife.”

“I think they did everything they possibly could to avoid this,” Gilmore said. “It’s unfortunate that we had to get to this situation.”

As CBS 2’s Suzanne Le Mignot reports, Stephon’s mother, Danelene Powell-Watts, arrived at the police station in Calumet City on Wednesday shortly before police held a news conference to discuss the shooting.

Powell-Watts was screaming, livid, and inconsolable after her son was killed. She was furious that officers used deadly force against her son this time, rather than subduing him with a stun gun.

“They shot my son,” she yelled as officers as she was blocked from entering the Calumet City police station. “Every last one of you know my son has autism.”

Gilmore said police had been called to the home 10 times since 2010 to deal with the boy. Stephon’s father called police again Wednesday morning after the teen had become aggressive.

“We tried to do everything we could to keep him from being a victim, as he was an offender. He chose to be an offender,” Gilmore said.

The chief said police were called to the home to get Stephon under control, as they had been before. But that didn’t work, he said.

“When he slashed the officer’s arm, the officer felt his life was in jeopardy and he had nothing else to do, but to defend himself,” Gilmore said.

Stephon’s family said police have used a stun gun on him in the past.

“They didn’t have to murder him. This is nothing but murder and they shoot to kill,” Powell-Watts said. “He had a butter knife and … my husband said that he lunged at the police officer.”

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Stephon’s uncle said police had subdued his nephew with stun guns before.

“They didn’t have to shoot him. They could have tasered the child. He’s only 15 years old,” Wayne Watts said. “They could have tased him, like they did him before, took him to the hospital and he would have been fine and that’s what I want to know. Why couldn’t they do that to him so that he could still be breathing with us right now?”

Gilmore said a stun gun wasn’t used because the lead officer did not have a stun gun.

Five officers responded to the Watts home after Stephon’s father called police, according to Gilmore. Two entered the house, heading to the basement where they found Stephon. One of those two officers did have a stun gun with him.

“Unfortunately today, when he slashed the officer’s arm, the officer felt his life was in jeopardy and he had nothing else to do, but defend himself,” Gilmore said.

The boy’s family said police should have used a stun gun and spared his life, especially since they’d been to the home before and knew what to expect.

Both officers have been placed on paid administrative leave.

Dr. Louis Kraus, professor and section chief of child and adolescent psychiatry at Rush University Medical Center, questioned whether deadly force was really necessary.

“With everything that they’ve done before, they should have known before going in what they were dealing with. And, you know, the goal really should have been to have gotten this child to a hospital,” Kraus told CBS 2’s Dana Kozlov.

He said people with autism can frequently become aggressive, but not because they are trying to hurt someone.

“What we know is that, when they get anxious – probably more commonly than they typical person when they get anxious – they might lash out; not with the intention of doing harm, but simply because of how frightened they are,” Kraus said.

Calumet City Ald. Brian Wilson had questions about the shooting as well.

“I think less deadly means could have been used,” Wilson said.

The alderman is staging a protest at 7 p.m. outside the Calumet City police station.

Meanwhile, Illinois State Police are investigating the shooting.

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Gilmore said a year ago, all of the officers in the department went through a three-day autism awareness program to learn how to handle calls involving people with autism.