Updated 02/02/12 – 6:14 p.m.

CALUMET CITY, Ill. (CBS) — Relatives and friends of a 15-year-old autistic boy who was shot and killed by police officers on Wednesday were voicing their outrage by staging a protest outside of the police station Thursday night.

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Local clergy, as well as some civic leaders, and autism support groups also joined demonstration to call for an independent probe of the shooting death of Stephon Watts, who suffered from Asperger’s Syndrome, a high-functioning form of autism.

“I do believe race played an important part of this – that if this had been done in a white community, the officers would have had a different attitude about how they approached this child, knowing that this child had autism,” said David Lowery, Jr., president of the NAACP’s Chicago Far South Side Branch.

Stephon was shot and killed by two police officers Wednesday morning after police were called to his family’s home because he had become aggressive.

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Police said he had cut one officer with a knife and was acting in a threatening manner, so officers shot him in fear of their own safety. But Stephon’s family said he was only holding a butter knife and that, in previous encounters, police had been able to subdue him with a stun gun, so officers could have done the same thing on Wednesday.

Others who joined the protest with the family Thursday night were the Rev. Jesse Jackson and Calumet City 4th Ward Ald. Brian Wilson.

Jackson said he has reached out to Illinois Attorney General Lisa Madigan, Cook County State’s Attorney Anita Alvarez and the U.S. Justice Department to call for an outside investigation of what he called “cold-blooded, wrongful and unnecessary use of force.”

Jackson said police could have grabbed Stephon and held him to bring him under control or subdued him with a stun gun, rather than resorting to deadly force.

“Why shoot him point-blank range with two bullets?” Jackson said.

He also said that, by the time police showed up at the house in response to the family’s call for help, Stephon had calmed down. The family told police they no longer needed assistance, but Jackson claimed officers forced their way into the basement and, when Stephon saw police, he became agitated again.

“We know that the police who did this must now face the challenge of justice,” Jackson said.

Wilson also said that officers should not have shot Stephon, given that police had been called to the Watts home at least 10 previous times when Stephon had become aggressive and had been able to calm him down or subdue him with a stun gun, rather than needing to use deadly force.

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“We want to wrap our arms around the family and let them know that we believe this was a disgrace. Their child should not have died yesterday,” Wilson said.

Police officers shot and killed Stephon after he lunged at them with a knife. The family said it was a butter knife and police would only say it was a “kitchen knife.”

“Less lethal forms of restraint should have been used yesterday and that’s what we want the message to be,” Wilson said.

Lowery said authorities should make sure there is a thorough, independent investigation of the shooting.

“My heart goes out to that family and we want to stand with this family and make sure that this is not swept under the rug, like it’s usually done when white officers kill a black child,” Lowery said.

Debra Vines, executive director and founder of The Answer Inc., an Autism awareness and support agency primarily serving families of color, said many families her group serves have said they fear that could have been them.

“That’s the first thing they were saying. That’s the first thing I thought. That could have been Jason.”

Vines’ son Jason was 11 years old when police were called to help, because of a medication imbalance. Jason is now 24 and thriving.

“Unfortunately, this was a tragic situation; but maybe what’ll happen is that they’ll start paying more attention to our community of people; they’ll start being more sympathetic to our community,” Vines said.

The Answer Inc. also provides training for police to educate them on how to handle calls involving people with Autism.  The organization is having a conference on Saturday March 24 from 10 a.m. to 2 p.m. at Rock of Ages Baptist Church in Maywood.  The event is called, “Celebrating Differences Autism and Special Needs Conference.”  The conference will have several workshops, including one for law enforcement called “To Serve and Protect.”

Admission and registration are free.

In response to the planned protest, the assistant chief of the Calumet City Police Department said everyone coming has the right to have a peaceful assembly and to express their opinions.

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The two officers who shot Stephon have been placed on paid administrative leave, and Illinois State Police are investigating the shooting.