A Colorado cold case that haunted investigators for more than two decades just saw a major breakthrough: a suspect was arrested in Iowa in connection with the 2003 killing of 29-year-old Rosa Arguello, a Hopi Tribe member whose body was discovered in Thornton.
Arguello was found dead on October 17, 2003, beside a roadway in the 12000 block of Quebec Street in Thornton, Colorado. Investigators said she had been stabbed multiple times.
For years, the case remained unsolved. But on September 15, 2025, police in Dubuque, Iowa arrested 55-year-old Robert McClain on a warrant out of Adams County, Colorado. Authorities say he is charged with homicide in Arguello’s death, and extradition to Colorado has been in progress.
The arrest that reopened everything
According to reporting from CBS Colorado, investigators with the Dubuque Police Department took McClain into custody on a Colorado warrant after receiving information that he may have been involved in the long-unsolved homicide.
Local Iowa reporting added that McClain was arrested Monday morning in Dubuque and is being held in Dubuque Police Department custody.
Thornton Police Chief Jim Baird credited the cross-state teamwork behind the arrest, saying the department was grateful for its partners at Dubuque PD and would continue working with the 17th Judicial District Attorney’s Office “to pursue justice for Rosa and her family.”
Who was Rosa Arguello?
Police and media reports describe Rosa Arguello as a 29-year-old woman who lived in Thornton with her children. She was also identified as a member of the Hopi Tribe, an Indigenous community based in Arizona.
Her death is one of many cold cases that have remained painfully unresolved for families for years — and the sudden movement in her case is a reminder that investigations don’t always stop when the headlines do.
What investigators are (and aren’t) saying
So far, authorities have not publicly laid out the evidence trail that led them to McClain, and investigators have been cautious about detailing how they connected him to the 2003 homicide.
However, CBS 2 Iowa reported that court records show Colorado investigators had been looking into McClain with assistance from Dubuque Police since October of the previous year. The outlet also reported that a search warrant was obtained for his home, and that he was charged with possessing a firearm as a felon.
What comes next will likely happen in Colorado courtrooms. If McClain is extradited, prosecutors in the 17th Judicial District will have to prove the case built from decades-old leads, documents, and forensic work — the kind of challenge that makes cold-case prosecutions difficult, but not impossible.