Federal investigators said a Minnesota man is accused of harassing as many as 60 women across the country over the internet, including several women in Colorado.

Court documents detail the accusations by four Colorado women. Several of the victims are CU Boulder athletes.

Investigators said Eric Bolduan, a software engineer, downloaded the victim's pictures from sites like Instagram and then found pornographic pictures of women who looked like them before uploading the photos to porn sites.

A spokesman for the U.S. Attorney's Office in Denver said some of the images were altered.

The criminal complaint said the victims started getting messages from different email accounts.

One of the messages reportedly told the victim that if she wanted to be left alone she'd either have to kill herself or leave college.

Another threatened to kill the victim. One woman was threatened with a detailed account of how she'd be stalked.

The suspect is accused of not only threatening them, but emailing some of their families and the university, according to authorities.

The U.S. Attorney's Office said that after some victims came forward, the FBI got involved. Federal agents tracked Bolduan to Rochester, Minnesota where he lives and carried out a search warrant in June.

According to the criminal complaint, Bolduan admitted to being responsible for harassing and threatening the four Colorado women as well as other victims.

Bolduan's criminal history goes back to 1993, when he was convicted of criminal sexual conduct in Minnesota and for indecent exposure in 2004.

"While the Defendant currently asserts a willingness to get mental health treatment, that willingness is countered by Defendant's failure over many years to obtain or to comply with effective or long-term treatment," court documents say.

Investigators said Bolduan set up multiple email accounts, identified hundreds of potential victims and targeted women randomly.

He's been extradited to the Denver area and is facing six felony charges including stalking.

CU Boulder did not comment since, saying they don't talk about open investigations.