WASHINGTON — A man who formerly lived in Fairfax, Virginia, has pleaded guilty to sex trafficking a 15-year-old girl.

The office of the United States Attorney for the Eastern District of Virginia said in a statement that Derek Leon Mantilla, 21, pleaded guilty Tuesday to a charge of sex trafficking of a minor.

Prosecutors believe Mantilla, along with Ismael Antonio Mendez and Caitlyn Ann Smith, recruited the girl to engage in commercial sex acts to pay off a debt that was owed to Mantilla by Mendez.

They add that the three adults taught the 15-year-old how to prostitute, took photos of her to use in ads and created ads that were posted on the Internet.

The three adults knew the girl was a minor and instructed her to lie about her age to customers in a number of states, including Virginia, the prosecutors said.

Between November 2014 and February 2015, the girl worked seven days a week and saw an average of 10 to 12 customers a night, prosecutors said.

Mendez and Smith have already pleaded guilty in the case.

Mantilla will be sentenced July 8 and faces a mandatory minimum of 10 years up to life in prison.