Police in the Denver suburb of Westminster said they arrested 17-year-old Austin Reed Sigg after getting a tip that led them to a home Tuesday night.
Sigg's residence is about five miles from the home of Jessica Ridgeway, who disappeared Oct. 5 after leaving for school. Her body was found five days later in a field at a park.
"We worked on this case nonstop, around the clock, since Oct. 5, the day of her abduction," Police Chief Lee Birk said at news conference. "I believe we've made a significant step towards justice for Jessica."
The break in the case came a day after police said Jessica's abduction was linked to the May 28 attempted kidnapping of a 22-year-old runner at another park, the Ketner Lake Open Space.
In that case, a woman fought off a stranger who grabbed her from behind and put a rag over her mouth that smelled of chemicals. Westminster investigator Trevor Materasso said Tuesday police haven't been able to determine if the substance on the rag was meant to subdue the woman.
Authorities didn't say why they think the two cases are linked, but they noted Sigg will be charged in both crimes. His first court appearance is set for 8 a.m. Thursday.
Reached by phone Wednesday, Sigg's mother told The Associated Press he turned himself in.
"I made the phone call, and he turned himself in. That's all I have to say," said Mindy Sigg, before she broke down in tears and hung up the phone.
It wasn't immediately clear if her call was the one that police said led them to Austin Sigg's home.
Authorities said they notified the Ridgeway family of the arrest Wednesday morning.
"We hope and pray that this arrest brings them some measure of closure in dealing with this enormous loss that they've suffered," Birk said.
Jessica was walking down a quiet street in her modest neighborhood when she was last seen alive. Her school backpack was found three days later in Superior, another Denver suburb about seven miles northwest of her home.
After her disappearance, more than 1,000 officers and 10 agencies, including the FBI, investigated the case, following up on more than 4,000 leads.
While authorities searched for her killer, high school students volunteered to walk younger students to class to keep them safe and more parents were waiting at bus stops with their children and dropping them off at school.
The number of suspected abduction attempts reported to police also increased, possibly because more children and parents were on alert for suspicious behavior.