PARKER, Colo. -- A former Parker youth pastor arrested on child sex assault charges began a sexual relationship with a member of his church's youth group when the girl was 17 years old, according to an arrest affidavit.

Joshua Clemons, 35, was arrested Tuesday by the Denver Police Department amid an ongoing investigation into allegations he sexually assaulted at least one member of the youth program he led at Crossroads Community Church. While the church is located in Parker, the alleged abuse occurred at Clemons' home in Denver.

Clemons worked as a youth pastor at the Parker church from 2006 through September 2015, the police department said.

The affidavit states that Clemons and the alleged victim knew each other since the girl was in fifth grade, but they didn't begin a sexual relationship until September 2014 – when she was 17 years old.

The alleged victim told police that Clemons had admitted to kissing two other girls in the youth group but police didn't provide any further details about those incidents.

The investigation began in February 2018, when the pastor at Crossroads Community Church informed police that the church learned of the relationship between Clemons and the alleged victim in December 2016. But Clemons claimed at the time that the affair didn't begin until October 2015, several months after the girl turned 18.

The pastor reported the case in 2016 because he was concerned that the relationship had actually started when she was a minor, the affidavit states. At the time, police said no crime had been committed.

The pastor then went back to police in February of this year after hearing from the alleged victim's mother, who was concerned that Clemons was being hired as a youth pastor by another church, according to a statement from church leadership.

In an interview with police a few days later, the alleged victim said she and Clemons first had sexual intercourse in June 2015 when she was a 17-year-old senior in high school, but they had kissed and had other sexual contact before then. Clemons was married at the time but told the girl that he wanted to divorce his wife to be with her, the affidavit states.

Clemons knew the girl was underage and even gave her a card with a message along the lines of "We're legal" on her 18th birthday, according to the affidavit.

The relationship continued when the alleged victim graduated from high school and enrolled at Colorado State University, the affidavit states. The alleged victim told police that Clemons visited her almost daily and the two continued to have sex regularly.

At one point, Clemons went to a pharmacy and bought Plan B - the so-called "morning after pill" -- and made the alleged victim take the medication.

The relationship ended in late 2017, the affidavit states, at which point the alleged victim said Clemons started "stalking" her and showing up at her new church. The alleged victim threatened Clemons with a restraining order, according to the affidavit.

In October 2017, the alleged victim was on a retreat with a different church when she decided to disclose the relationship for the first time, according to the affidavit, and the person she told decided to report the relationship since she was concerned that Clemons may still have access to young girls.

In a letter to the congregation, Crossroads Community Church leaders said the church conducts background checks on all new hires and repeats those checks every two years but in light of the allegations, leaders would be reviewing policies to prevent anything similar from happening in the future.

Parker and Denver police are looking for any possible further victims or witnesses to the alleged abuse. Anyone with information is asked to contact Parker Police Detective Wilson at 303-805-6561 or via email at bwilson@parkeronline.org.