Kayleah Wilson's body was found last week after she went missing on March 28 as she walked to a friend's birthday party. Police say her death was not accidental.
That same day, Greeley Police arrested 18-year-old Robert Montoya on charges of sexual assault on a child. In his arrest affidavit, he admits to having sex with an underage girl. That girl told friends she was possibly pregnant.
The arrest affidavit makes it clear why he is charged with sexual assault. In the affidavit, names are blacked out.
The affidavit says Montoya moved in with his girlfriend and her mother in October 2009. Montoya and his sister had to move out of their home because Montoya's mother wanted to begin a relationship with a registered sex offender, Jonas Garcia, and Garcia was not allowed to be around children, according to the affidavit.
The mother of the alleged victim told police she assumed Montoya and her daughter were good friends at first, but that she began to see signs of a physical relationship between the two of them in December.
According to court records, one of the dates of sexual contact between Montoya and Kayleah was in December.
Police say Montoya also claimed that during sex, the alleged victim wanted him to physically abuse her, but he did not.
The mother of the alleged victim told police she confronted Montoya and he admitted he and her daughter had been having sex and they considered themselves boyfriend and girlfriend, according to the affidavit.
When the mother of the alleged victim confronted Montoya, she told him to leave their house.
The affidavit says the alleged victim was very angry initially, but then stopped talking about the relationship.
According to the affidavit, Montoya admitted he tried to see the alleged victim without her mother knowing several times.
The affidavit says she caught them at an abandoned car dealership in February.
Later, the affidavit says he would even hide in the bushes outside her home went to her school.
When the alleged victim caught him doing that, she called him a "stalker freak" and told him to leave her alone, according to the affidavit.
Montoya faces felony charges including sexual assault for allegedly having sex with Kayleah. He is in jail, being held on $10,000 bail.
Click here to read the entire arrest affidavit.
9NEWS spoke with Montoya's family, but they had no comment.
He is not charged in Kayleah's murder and police have not named him a suspect in that investigation.
Greeley Police are still looking for additional tips related to Kayleah's homicide investigation. Anyone with information is urged to call 970-350-9600. There is a $20,000 reward for information that leads to an arrest and conviction.
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