The 28 charges against O'Leary include second-degree kidnapping, sexual assault, burglary, stalking, theft and possession of burglary tools.
O'Leary was officially charged in connection with four incidents in Jefferson and Arapahoe counties in February. The Jefferson County District Attorney's Office says O'Leary sexually assaulted three women, one in Golden, one in Aurora and another in Westminster, and attempted to sexual assault a woman in Lakewood.
"This is one of the most extreme cases we've ever seen," Robert Weiner with the Jefferson County District Attorney's office said. "Thankfully we don't see this type of offenders often, but when you do, you're thankful that you have such good law enforcement officers to handle the case."
The guilty plea came as part of a plea deal with the DA's office.
"We felt like in light of all of the circumstances that we weren't really giving anything up and in deference to the victims - not traumatizing them any further," Weiner said.
The DA's office says one of the sexual assaults happened in Westminster in the summer of 2010. Another one occurred in Golden in January 2010. Both police departments found similarities in the two cases.
In the Golden case, a woman was attacked at the Summit View Apartments. The suspect waited outside the victim's apartment, broke in and assaulted her.
In the description of the suspect, police said he had a tattoo or mark on his leg that looks like a large chicken egg.
Jefferson County District Attorney's office spokeswoman Pam Russell said the woman "in [the Lakewood] case was able to escape and then he fled before he was arrested. The case had been open and pending until these other investigations had drawn in investigators from not only other law enforcement agencies in the metro area, but the CBI and the FBI."
Aurora Police told 9NEWS they also had a case that could be linked to O'Leary. An Aurora woman was sexually assaulted in October 2009.
In February, when asked by the judge if he had anything to say, O'Leary replied, "These charges are erroneously filed against a person who is not myself."
O'Leary will be extradited to Washington state to face charges in two cases there. After sentencing in Washington, he will return to Colorado to face sentencing on Dec. 12.
At his sentencing hearing, he could be sentenced to a period of over 100 years or life.
Resources for victims of sexual violence
Some of the biggest myths are that most violent acts are random and unpredictable and that women are defenseless.
In fact, women have a powerful weapon to fight back, according to Gavin De Becker, author of the book, "Gift of Fear."
"More than almost every other creature on earth, women have a brilliant internal guardian, a nuclear defense system: intuition. Human intuition is the result of millions of years of refinement and development - more impressive than the most powerful computer. Women are not defenseless," wrote De Becker in an email to 9NEWS.
The book describes techniques that predators use to get women to let down their guards and trust them.
It's been required reading for many law enforcement agencies in Colorado because it also helps officers determine if people might become violent.
Denver Police Lt. Matt Murray has incorporated parts of the book with his own philosophies when he travels across the country to teach officers how to handle domestic violence issues and stalking for the organization the International Association of Chiefs of Police.
"The number one thing is to be aware. Think about where you are. Don't be under the influence. If you're intoxicated, make sure someone is going to take care of you. It impairs our ability to make good decisions," Murray said.
Murray also teaches free self-defense classes for young ladies and women at the Denver Police Department under a program by Chief Gerald Whitman.
He says women need to be alert, just like police officers, to what and who is around them.
According to Murray, the statistics of police officers getting robbed or mugged while off-duty are next-to-nothing because of the way officers carry themselves, look people in the eyes and pay attention to what's going on around them.
Many of those techniques are taught by Bill Kipp, owner of FastDefense in Colorado. His program shows women how to be assertive to prevent becoming a victim and then, if all else fails, how to fight back using the power of their adrenaline.
Rape Assistance and Awareness Program is a rape crisis center in the Denver metro area that offers counseling. Victims can call the program's 24-hour hotline at 303-322-7273.
FAST Defense is a program that offers self defense classes. Call 720-256-3898 to learn more about the classes.
The Gift of Fear is a book that aims to help people look out for dangerous situations.
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