At approximately 10:51 a.m. on Monday, September 15, 2025, officers and investigators with the Dubuque Police Department arrested 55-year-old Robert McClain, of Dubuque, on a warrant out of Adams County Colorado charging McClain with Homicide.
Dubuque Police previously received information that McClain may be involved in a Colorado homicide cold case. This information was provided to the Thornton, Colorado, Police Department. Thornton Police conducted an investigation, with Dubuque Police assisting where requested.
The case is in connection with the murder of 29-year-old Rosa Arguello, a member of the Hopi Tribe, whose body was found stabbed to death in a Thornton field in October 2003.
The investigation stalled for two decades until new information received by Dubuque police in late 2024 suggested McClain was connected to the homicide. This led to a search warrant for his home and ultimately, his arrest.
McClain is currently held in Dubuque while awaiting extradition to Adams County, Colorado.
According to court records and online reporting, McClain has a prior criminal history, including an attempted murder charge in 2014 for which he later pleaded guilty to lesser charges and served 15 years in prison.