One of three men involved in a violent bank robbery on Chicago's South Side has pleaded guilty to charges that could land him in prison for 20 years.

Alton Marshall is the second of the trio to enter a guilty plea. Marshall on Thursday also agreed to testify against David Vance, the third suspect accused in the May 22, 2007 shootout that killed bank teller Tramaine Gibson and wounded two security guards. Vance has pleaded not guilty.

The bank teller's father, Verton Gibson Jr., was in court Thursday to argue against the plea deal. He told U.S. District Judge Joan Gottschall a 20-year sentence for the 32-year-old Marshall would be too lenient.

Gottschall said she would wait to read more materials before accepting Marshall's plea.

Last month, a second suspect, Henry Bluford, entered a guilty plea.