DENVER (CBS4) – CBS4 has learned a man accused of being a serial rapist was arrested while driving a high-profile Colorado politician’s car.

William Costello, 47, was formally charged on Monday with two counts of second-degree kidnapping, two counts of sexual assault on a child, three counts of sexual assault, and two counts of impersonating a peace officer.

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But well-known political consultant Mike Stratton told CBS4 he was stunned to hear Costello, a person he’s known for several years and has worked with, is accused of such serious crimes.

The Democratic Party says Costello has never worked for the party.

William Costello (credit: Denver DA)

William Costello (credit: Denver DA)

A physical fight with an elderly man in a King Soopers parking lot netted Costello a felony assault charge in July of this year. He was later arrested in the town of Bayfield for the assault. From there Katie’s Law and his DNA linked him to three other crimes.

Arrest documents from Bayfield town marshals say Costello, a real estate broker, was driving Stratton’s car when he was arrested in the small southwest Colorado town. The car was impounded.

“Mr. Costello was in the area given direction by Democratic politician Mike Stratton to deliver campaign signs to the Democratic office in La Plata County,” Bayfield Marshal Joseph McIntyre told CBS4.

Police have not yet released Costello’s photo while they conduct witness lineups.

“Here in Denver, this is one of the most significant offenses that we’ve had,” Denver District Attorney Mitch Morrissey said.

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Passed in 2010, Katie’s Law allows DNA to be collected after a felony arrest and charge. The DNA can then be compared against a criminal DNA database even if there is no felony conviction.

“Three unsolved sex assaults out of Denver came up as a match to his DNA,” Morrissey said.

The first case in 2008 involved a 13-year-old runaway who police believe Costello picked up near 16th and Bellaire. According to court documents, the girl says there was a 2-year-old boy in the backseat while she was raped.

The second case is from 2010. A 22-year-old woman claims she wanted a ride through a fast food drive-through near Colfax and Krameria and climbed in to a car with a stranger. Instead of taking her to the restaurant, the woman says she was raped in the back seat by a man who claimed he was a police officer.

The final case was in 2011. A woman waiting for a bus near 32nd and Federal says she was ordered to get in to a car by a man with a gun also claiming he was law enforcement. She too was raped inside the car.

Morrissey says without Katie’s Law the cases may have gone unsolved.

“To see it actually have an impact on this type of case, it’s very, very important to us,” he said.

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Costello made his first court appearance Tuesday morning. He’s being held on a $200,000 bond.