Woman killed, allegedly by her son in San Tan Valley. Niece says she thought it was a "sick Halloween joke"

SAN TAN VALLEY, Ariz. - A family member of a woman who was killed, allegedly by her own son, is speaking out about the tragic ordeal.

The body of 38-year-old Mary Collier was found Wednesday morning in a field in San Tan Valley.

The investigation included a fake kidnapping call made by the son, according to authorities. 

The family is still coming to grips with this. 

It's an almost unheard of crime, losing one loved one, allegedly at the hands of another loved one. 

READ MORE: Woman found dead in San Tan Valley; son accused of murder: PCSO

"She was such an incredible human being," Rebecca Hatch said through tears. 

Rebecca Hatch was her niece. 

"I didn't believe it at first"

Collier was found by a jogger Wednesday morning, Oct. 30 in a San Tan Valley field. 

Investigators believe her 18-year-old son killed her.

"I didn't believe it at first. I thought it must be some kind of prank, some kind of sick Halloween joke," Hatch said. "Tragically, it turned out to be true."

"She was so passionate about her faith"

Her aunt was the caretaker of the family, putting everyone else's needs above hers and relying on her faith to make it happen, according to Hatch. 

"She was a Mormon. That's something I think she would want people to know. Mary was a Mormon in the strongest sense of the word. She was so passionate about her faith. She's so devoted to it, and she touched the people around her and she inspired them with the way that she was. She was selfless," Rebecca says. 

The big question is why? Rebecca says the family cannot begin to understand, especially since the mother and son always seemed so close. 

"Of all the people in the family, Mary was the one he loved the most; she was the one he respected the most. It's inexplicable. It is completely incomprehensible, and it comes completely out of nowhere," Rebecca says. 

She adds that the entire family will come together soon and find a way to move on, honoring Mary's life by following in her footsteps.

"I'm sure that if I could've heard her last word, it would've been about her family, about the people that she loved," Rebecca said. "That's the kind of person that she was."

Collier was found by a jogger in a farm field west of Gantzel Road and south of Skyline Drive at around 9 a.m. on Wednesday. Her body was in an open field and behind piles of dirt.

Her cause of death is believed to be from blunt force trauma from a sharp object.

Investigators said they believe the killing stemmed from an argument on Tuesday night that carried on into Wednesday morning. They did not, however, determine a motive for the crime.

For those looking to help the family going forward, a GoFundMe was established to raise money for her funeral.