Colorado Murder Case Busts Open in Dubuque After 20 Year Wait

For over two decades, a certain murder cold case has weighed heavily on the community of Thornton, Colorado. Now, there may finally be some answers and justice on the horizon after a recent arrest in Dubuque, Iowa. On Monday morning, September 15th, the Dubuque Police Department arrested 55-year-old Robert McClain on a warrant issued out of Adams County, Colorado.

He is being charged in connection with the 2003 murder of Rosa Joan Arguello.

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Arguello, 30, a member of the Hopi Tribe, was found dead on October 17th, 2003, in a ditch near the 12900 block of Quebec Street in Thornton. She had been stabbed multiple times. For years, the case remained unsolved, with limited evidence and no arrests.

In late 2024, Dubuque Police received new information that suggested McClain could be linked to the homicide. That lead was shared with the Thornton Police Department, which reopened its investigation. Working with Iowa authorities, investigators obtained a search warrant for McClain’s home. Evidence collected during the investigation ultimately led to Monday’s arrest.

Officials from Thornton Police explained that their team has been collaborating closely with prosecutors in Colorado to prepare the case. They emphasized the importance of pursuing accountability, not only to honor Rosa’s memory but also to bring long-awaited closure for her family and community.

McClain is currently being held in Dubuque while arrangements are made for his extradition to Colorado. Once extradited, he will face prosecution in Adams County. Law enforcement is continuing to encourage the public to come forward with any information that could assist the case. Even after two decades, they note, community tips can make a difference in strengthening the investigation and ensuring justice is served. Those with information can contact the Thornton Police Department at (720) 977-5124.