I learned today that there has been a development in this case. Iowa City Patch reports that there has been an arrest in this case. The man arrested is not the robbery suspect himself, but instead a transient accused of keeping watch while the robbery occurred:
According to an Iowa City police criminal complaint, Daveon Curry, 19, address unknown, was arrested and charged with first-degree robbery, joint criminal conduct, and assault with the use or display of a weapon for allegedly serving as a lookout while another man threatened a female cashier with a knife and made off with several hundreds of dollars in cash...Seeing how a "co-defendant" is mentioned but not identified, it would not surprise me if a second arrest isn't made soon.
Both Curry and the co-defendant stated to the police that Curry was there acting as a lookout at the crime, according to the criminal complaint. Curry allegedly received $40 as his cut for his role in the crime.