WESTMINSTER — The police search for the killer of 10-year-old Jessica Ridgeway led them just a mile from where it began, to the home of a teenager with an aptitude for crime-scene forensics and an interest in mortuary science.

Authorities arrested Austin Reed Sigg, 17, who lived about 1½ miles from Jessica in a neighborhood near Ketner Lake. The arrest was made Tuesday evening after Sigg’s mother called authorities and he turned himself in.

“Today, I believe we have taken a significant step toward justice for Jessica,” Westminster police Chief Lee Birk said. “We hope and pray that this arrest gives (the family) some measure of closure.”

The family’s pastor, Rick Long of Grace Church in Arvada, said that for Jessica’s mother, Sarah, the arrest “begins another phase of the nightmare.”

The news is a “Catch-22” for the family, he said, meaning they are glad to have Sigg off the street but will now have to endure new details of the gruesome crime being made public.

“I’m so saddened,” Long said. “We’re talking about a 17-year-old. I just feel sick for everyone involved.”

Jessica’s paternal great grandmother said that while she is saddened for Sigg’s family, she is struggling to contain her anger at him.

“I think it’s all I’ve got within me not to just want to just burn him,” Donna Moss said during a press conference Wednesday in Independence, Mo. “I meant literally light him on fire. Send him to hell in a blaze of glory.”

Jessica’s father, Jeremiah Bryant, stood silently behind Moss as she spoke. He declined to address reporters, according to KCTV television.

Jessica’s mother and other Colorado relatives, through Westminster police investigator Trevor Materasso, said they did not wish to make a statement to the media. He also said he would not talk about the case.

Sigg, described in arrest papers as “cooperative,” was being held Wednesday at the Mount View Youth Services Center in Lakewood, which houses juveniles charged with crimes.

He is due in Jefferson County court Thursday morning, where he will be advised that he is being held on suspicion of first-degree murder, felony murder and kidnapping in Jessica’s case, and on suspicion of criminal attempt to kidnap and murder in an attack on a jogger at Ketner Lake.

“Justice for Jessica is a process,” Jefferson County District Attorney Scott Storey said. “This is the beginning of that process.”

As a 17-year-old, Sigg can be tried and, if convicted, punished as an adult in the case, and Storey’s office said they would try him as an adult. But, after U.S. Supreme Court rulings in other cases, he would not be eligible for the death penalty or a mandatory life term without parole.

No details of the evidence against Sigg were released, and documents already filed in the case have been sealed.

Birk and Storey both emphasized that, though Sigg had been arrested, the investigation remained underway. They released a photograph of Sigg and asked for phone calls to 303-658-4336 from anyone who had seen him since Jessica’s disappearance Oct. 5.

Jessica’s backpack was discovered two days later and 6 miles away. Her dismembered body was then found Oct. 10 in a bag in an Arvada field 9 miles from her home.

Authorities warned that a predator was on the loose in the area and, with help from the FBI and Colorado Bureau of Investigation, worked nearly around the clock to find the killer.

Then, Tuesday evening, a call came to police.

“I made the phone call, and he turned himself in,” Sigg’s mother, Mindy, told The Associated Press. “That’s all I have to say.”

After his mother consented, Sigg was interviewed by investigators for six hours, sources told 9News.

On Wednesday afternoon, much of Sigg’s neighborhood was cordoned off with police tape. While news helicopters circled overhead, investigators took a brown Jeep Grand Cherokee with a NASA decal on the back windshield away from his home at 10622 W. 102nd Ave. They pored over a construction trash bin across the street and could be seen working in the backyard.

Investigators told The Post that they found “DNA remnants” in the crawl space of the home.

Sigg, who years earlier had attended the same elementary school as Jessica, was a student at Standley Lake High School through 11th grade before leaving to complete his GED at Warren Tech. There, he worked toward a career in health occupations or forensic science and won second place in the spring in a Health Occupations Students of America competition in the category of crime-scene investigation.

He then enrolled this fall at Arapahoe Community College, where a classmate said he was majoring in mortuary science.

Jacqueline Miller was in the same Psychology 101 class as Sigg. She said he wore a cross on a necklace and always carried a Rubik’s Cube.

Miller said that at the start of the class in August, the professor asked the students for their majors. Sigg, she recalled, announced that he was majoring in mortuary science.

“He said he was intrigued by dead bodies,” she said. “There was something creepy about him.”

Authorities last week released a photograph of a small wooden cross, saying it may be connected to the killer.

Brooke Roble, a freshman at Standley Lake, lives seven houses away from Sigg and has known him all her life. The two used to get into play fights where they’d throw knives at each other, and she said Sigg had a large collection of switchblades, pocketknives and other blades.

She said Sigg was into music and computers and excelled even in advanced courses. She said he had always been “a total sweetheart” and a favorite of teachers.

“If you were walking by yourself, he would be the one to come up to you. He knew everybody,” she said. “This was really shocking. I didn’t expect it.”

Brooke said the school brought in counselors Wednesday and pulled Sigg’s younger brother, a freshman, out of class before the news of the arrest became public.

Sigg left high school to get his GED not because he was in any trouble but because he was ready to move on, Brooke said.

Standley Lake senior Elexus Parmiter, 17, went to school with Sigg starting in elementary school.

Wednesday, she was at home during lunch when she saw the news. “I hope he didn’t do it, honestly, I hope the best for him still,” she said.

Parmiter and another friend Ashley Philbrook, 18, described Sigg as sweet and “very smart.”

News of his arrest immediately eased the concerns of parents in the neighborhood, who for weeks had believed there was a predator in their midst, not knowing he was a neighborhood teen.

Neighbor Lexi Thornton, mother of a 3-year-old girl, said she has been afraid to be outside since Jessica disappeared.

“It’s been terrible,” Thornton said. “God bless the Westminster police department. They’re amazing.”

Chuck Murphy: 303-954-1829, cmurphy@denverpost.com or twitter.com/cmurphydenpost

Staff writers Eric Gorski, Christopher N. Osher, Ryan Parker and Yesenia Robles contributed to this report.