Tenn. Man Accused of Killing 14-Year-Old Brother with Asperger's as Mom Walked Away Without Helping

Facebook Sayeed Neilson

A 14-year-old boy with an autism disorder died after a beating by his stepbrother that was witnessed by the victim's mother, who told the 33-year-old alleged assailant to quit but, according to police, admitted to "walking away without ensuring that he did stop."

The teen, Sayeed Neilson, was declared dead at the family's Nashville, Tennessee, home the next day after his mother placed a 911 call reporting him to be unresponsive.

The victim "didn’t deserve any of this,” said Neilson's aunt Rachel Duncan, reports KXAN. “He’s supposed to go on his first date and have his first kiss. He never got any of that, and it’s not fair.”

The mother, Rebecca Greenwood, 52, and her other son, David Matheny, both have been charged with criminal homicide, aggravated child abuse and evidence tampering. They remain in the Davidson County jail without bond, PEOPLE confirms.

Online jail records do not list an attorney for either of the accused, and it could not be determined if either one had yet entered a plea.

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Greenwood and Matheny initially said Neilson fell in the shower and hit his head on Oct. 22, police said in a statement. They said Matheny helped Neilson to his feet, helped him dry off and then assisted him into bed.

Greenwood and Matheny later left for a bar, but the mother told officers they checked on Neilson several times before heading out.

Metro Nashville Police Department Rebecca Greenwood, at left, and David Matheny

The next morning, Greenwood and Matheny said they went to a grocery to buy cleaning products, and then cleaned the house before discovering Neilson unresponsive in his room, according to police. Greenwood placed her 911 call at 11:50 a.m.

But detectives said Neilson's injuries were inconsistent with a fall.

Taken to police headquarters and interviewed, "Greenwood admitted to seeing Matheny punch Neilson and kick him in the head," according to the police statement. "She admitted to telling Matheny to stop the assault before walking away without ensuring that he did stop. Matheny, during his interview, admitted to having an altercation with his stepbrother, but denied causing him serious injury."

"Detectives believe the defendants’ cleaning of the house was related to destroying or limiting the availability of evidence," police said.

The victim's aunt said of Matheny, “The more you get to know him, he’s a narcissistic bully. A domineering kind of personality that always has to have his way, always has to be right, always has to be in control,” reports KXAN. She said Greenwood was afraid of him.

She said her nephew, who had just enrolled in high school and for the most part was like any other child his age while living with Asperger’s, an autism spectrum disorder, loved Halloween and Star Wars.

“I just wanted to know, why?," Duncan told KXAN. "Why didn’t you protect him? Why didn’t you call someone?”

“That’s your baby," Duncan said of Greenwood. "You should always protect your child. I know it’s both her kids, but Sayeed was a baby, only 14 compared to his older brother, who is 33.”