A former math teacher at Fort Zumwalt Middle School in St. Charles County has been sentenced to 20 years in prison for secretly videotaping dozens of young boys as they undressed at summer camp.

The St. Louis Post-Dispatch reports that 39-year-old Matthew Hansen of Winfield was sentenced Thursday after pleading guilty in federal court to eight counts of attempted production of child pornography.

Hansen was a counselor at an outdoor education camp in Cuivre River State Park as well as a volunteer firefighter. He videotaped as many as 80 boys, most under 12, between 2007 and 2012.

He was previously sentenced in Lincoln County to seven years in prison for possession of child pornography. That sentence will run concurrently with the federal punishment.