Published: Jan 31, 2014 3:14 PM EST

LEE COUNTY, Fla. - North Fort Myers residents Alan Robert Johnson, 35, and Jennifer A. Sparks, 39, pleaded guilty earlier this week to production of child pornography.

Johnson faces a mandatory minimum penalty of 25 years, up to a maximum penalty of 50 years in federal prison.

Sparks faces a mandatory minimum penalty of 15 years, up to a maximum penalty of 30 years in federal prison.

A sentencing date has not yet been scheduled.

According to the plea agreement, on or about May 12, 2012, in Lee County, Johnson and his girlfriend Jennifer Sparks knowingly used a 4-year-old girl to engage in sexually explicit conduct for the purpose of producing child pornography. On June 4, 2012, a private citizen turned the cellular telephone that Johnson and Sparks had used to produce the child pornography over law enforcement. The cell phone had been found in a shopping cart at a Lee County Wal-Mart, on or about June 2, 2012.

Further investigation revealed that Johnson was a registered sex offender. A subsequent search warrant was obtained for his residence, and another cellular phone was located in the bedroom shared by Sparks and Johnson. That cellular phone also contained sexually explicit images of the minor.

This case was brought as part of Project Safe Childhood, a nationwide initiative launched in May 2006 by the Department of Justice to combat the growing epidemic of child sexual exploitation and abuse. Led by the United States Attorneys' Offices and the Criminal Division's Child Exploitation and Obscenity Section (CEOS), Project Safe Childhood marshals federal, state, and local resources to locate, apprehend, and prosecute individuals who sexually exploit children, and to identify and rescue victims. For more information about Project Safe Childhood, please visit www.projectsafechildhood.gov.