Editor's note: Video is from Feb. 6, 2019

PORTLAND, Ore. -- A Yamhill County photographer was charged Wednesday with six counts of child pornography production by the United States District Attorney's Office in Oregon.

It's the latest set of charges against 52-year-old Robert Arnold Koester. He also goes by the names Bert Kay, Rhake Winter and Qitooly, according to the U.S. District Attorney's Office.

Koester is a suspected serial sexual predator who authorities say took nude photos of models and sexually assaulted many of them, including some minors. The alleged criminal behavior occurred in Oregon and California. Authorities said Koester may have been committing these criminal acts as far back as 1994. He was arrested in November of 2018.

RELATED: Suspected serial predator charged with multiple sex crimes in Oregon

Wednesday’s charges stem from criminal behavior the U.S. District Attorney’s Office said began in January 2015. Koester is accused of coercing six minors in Oregon to “engage in sexually explicit conduct for the purpose of producing a visual depiction of such conduct,” according to the district attorney’s office.

Koester faces dozens of additional state and federal charges in Yamhill County and Carlsbad, California.

In November of 2018, following his arrest, Koester was charged in San Diego County Superior Court with six felony counts involving sex crimes against minors. A week later, 35 related state charges were filed against Koester. In February, he was charged with 32 related felony charges in Yamhill County Circuit Court. In March, he was charged with two counts of producing child pornography by the U.S. Attorney’s Office in the Southern District of California.

Federal law enforcement has been working with local law enforcement in Yamhill County, Carlsbad and across the country to help identify any additional victims. The case has been investigated by FBI in Portland and San Diego, the Yamhill County Sheriff’s Office and the Carlsbad Police Department.

Anyone who has information about the investigation or knows someone who may have been a victim is asked to complete a secure and confidential online questionnaire

Information and tips from the public can be emailed to modelcase@fbi.gov.

Additional information about the case can be found here