Co-defendants Brandon Alto and Christopher Harper were romantically involved, according to a longtime friend and Alto's Facebook page.
During that time, between October 2014 and August 2015, prosecutors said the men molested the same three children.
Brandon Lightcloud Alto, who was charged with more than two dozen felony counts of lewd acts against children, pleaded not guilty in an El Cajon courtroom Monday.
Alto lived in Alpine and attended Cuyamaca College and Granite Hills High School according to his Facebook page.
He also spent years behind bars as a juvenile for a separate case.
"Life was so much easier behind bars...it's been tough being heart somedays it feels like I have no one in my corner," he wrote on his Facebook page.
NBC 7 confirmed Alto spent time at Southern Youth Correctional Reception Center and in 2015 pleaded guilty to a "possession of child porn" charge.
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Another defendant in the case, Christopher Harper, faces similar charges. Harper was arrested last week and arraigned on Friday.
Harper was a fugitive wanted on three counts of sex crimes against children. He was found in Simi Valley Thursday and now faces at least nine counts of sex crimes with minors.
The relationship between Alto, Harper and their alleged victims is unclear.
Harper is being held at a separate detention facility in Otay Mesa.
Both men could face 15 years to life if convicted. Alto and Harper are each being held on $2 million bail.
