The accused child killer has been described by some friends as "a good guy."
9Wants to Know spoke exclusively with Sigg's ex-girlfriend, Danni, who is having a hard time coming to grips with what he is accused of.
At her mother's request, 9Wants to Know agreed to hide Danni's face and change her name, for her protection.
"The Austin I knew would never have done anything like that," Danni said. "He was my first boyfriend. He was my first kiss. He was my first date."
Danni says she dated Sigg twice, first when he was an 8th grader at Wayne Carl Middle School and again when he was a freshman at Standley Lake High School.
"He was so sweet and so kind. I know that heart is still in him. But sometimes things happen that change people," Danni said.
She says they first met at Warehouse: 180 in Arvada, which is a gathering place for Christian teens.
It may help explain the small wooden cross Westminster police call a vital clue.
"We went to church together. It wouldn't surprise me if he wore a cross. He always wore a necklace similar to the one in his mug shot," Danni said.
Danni says they never went to the same school and drifted apart two years ago, after they broke up.
She can't remember any warning signs, but says Sigg did have a collection of weapons.
"I knew he had a sword collection in his room or a knife collection or whatever. But it was his man cave. A lot of people collect stuff," Danni said.
JOGGER HAS ENCOUNTER WITH SIGG
A more recent encounter with Sigg left a very different impression on Christie Mueller.
Mueller says she ran into Sigg twice on a trail near Standley Lake, and he stared at her in a way that made her extremely uncomfortable.
She says, both times, Sigg was with two friends.
"It just really freaked me out," Mueller said. "When I saw them I just felt automatically like they were up to no good. It hit me. I almost fell over seeing his picture. It brought me back to seeing him here and it just being so close."
She always walks the trail with her dog.
"I think he's my protector. I think if he hadn't been with me that day, I just wonder what would have happened," Mueller said.
Danni wrote the following letter to Sigg:
"Austin, whatever happened and changed that broke you, I'm sorry for. I just want you to know that I'm praying for you. You aren't a bad guy. But you did a bad thing. I don't hate you. I wish I could see you and tell you that you're loved. I'll never stop praying for you and you've always got a place in my heart."
In the letter, she also quoted a Bible verse, First Peter, Chapter 4, Verse 8:
"Above all, love each other deeply because love covers a multitude of sins."
Danni says she began sobbing uncontrollably and had to leave school early when she learned Sigg was the suspect, even though she says they haven't spoken in more than a year.
She wants his family, and Jessica Ridgeway's family to know, she's praying for them as well.
"Sometimes the person that you once knew isn't the same person as they are today," Danni said.
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