Story highlights Formal charges against Austin Reed Sigg, 17, expected to be filed Monday

Jessica Ridgeway, 10, disappeared on her way to school on October 5

One of her great-grandmothers expresses her outrage over the murder

Jessica Ridgeway's suspected killer is a 17-year-old neighbor who authorities plan to try as an adult, officials in Colorado said Wednesday.

Formal charges against Austin Reed Sigg, a high school student who lived about one mile from the 10-year-old and her family, likely will be filed Monday, Jefferson County District Attorney Pam Russell said.

As a general policy, CNN does not show the booking photo or name suspects who are juveniles, but in this case, police had mentioned Sigg's name and released his photograph in hopes the public could provide information related to the case.

Sigg will face murder and kidnapping charges in death of Ridgeway, who was found a few days after she disappeared on her way to school on October 5. Her body -- which was "not intact," according to police -- was found at a park in Arvada, a Denver suburb just five miles from the family's home in Westminster.

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"We hope and pray that this arrest gives them some measure of closure in dealing with this horrible loss and tragedy they have suffered," Westminster Police Chief Lee Birk told reporters.

Ridgeway's family was told Wednesday morning that an arrest was made, police said.

One of her great-grandmothers said she feels like she wants to set the suspect on fire.

"I don't think I can look at this person, into his face and not be judgmental," Donna Moss told reporters outside her home in Independence, Missouri. "I think what I have, it's all I've got within me to not want to just burn him. And I mean burn him."

A warrant was served Wednesday at Sigg's home. He will have his first court appearance at 8 a.m. Thursday.

Police said a tip led them to Sigg's home, police said in a news release.

That visit allowed police to make an arrest in the Ridgeway case, as well as another case -- an attempted abduction near Ketner Lake.

Sigg also will be charged with attempted kidnapping and attempted murder charges, the district attorney said.