Bolduan sent messages to the victim stating his intent to spend his free time "hunting you," the U.S. Attorney's Office said.
Using an "anonymizer," which disguised his identity, Bolduan sent emails, text messages and posts to other victims — and their friends, family members and other students — at other universities and high schools in the United States, according to the U.S. Attorney's Office.
In November, the Denver Post reported Bolduan's alleged victims included at least three University of Colorado athletes and as many as 50 women across the United States.
"The victims in this case experienced real and profound suffering because of the acts of this defendant," United States Attorney Jason Dunn said in a statement. "It's possible that more young women have been victimized but just haven't been able to identify their assailant. We encourage anyone who has experienced this kind of threat to call the FBI."