A nurse and correctional officer at the Anamosa State Penitentiary were killed Tuesday morning after an inmate assaulted several staff members, officials said.Iowa Department of Corrections said in a brief statement it was investigating the assault, which took place about 10:15 a.m. in the prison infirmary. The department did not say whether the inmate used any sort of weapon in the attack.The victims have not been identified, pending family notifications and the investigation, the department said.The inmate — who also was not named — was restrained by security staff.