A Ponchatoula man faces 15 to 40 years in prison for downloading more than half a million images of child pornography — one of the largest collections ever found in the state, the U.S. Attorney’s Office said.

Robert Swan, 52, pleaded guilty Thursday for his role in a massive child porn network that included pictures and videos of children as young as 4 weeks of age being forced to engage in sexually explicit conduct, U.S. Attorney Kenneth Polite said in a news release.

Authorities found the pornography during a January 2013 search of Swan’s home at 39790 W. Sam Arnold Loop, where they seized 15 devices including computers, hard drives and flash drives. Swan shared the images through peer-to-peer programs over the Internet, Polite said.

Agents also found evidence that in January 2010, Swan and an associate, Thomas Middleton, forced a then-3-year-old girl to engage in sexually explicit conduct, which Swan recorded, Polite said.

“Robert Swan is every parent’s worst nightmare,” Attorney General Buddy Caldwell said. “In this case, our forensic examination revealed that Swan not only possessed or shared half a million images depicting the sexual abuse of children, but also that he actually teamed up with another pedophile to abuse an innocent child.”

Because of a 1987 conviction for lewd and lascivious assault of a minor in Escambia County, Florida, Swan faces a mandatory minimum sentence of 15 years and a maximum of 40 years, followed by lifelong supervised release, Polite said.

Swan also faces a $250,000 fine and can be required to register as a sex offender.

Swan’s sentencing is set for March 25.