Prison officials say a staffer smuggled contraband into the Iowa State Penitentiary in Fort Madison, prompting a lockdown.

Fred Scaletta, executive officer for the Iowa Department of Corrections, says in a statement Thursday that the security breach is under investigation and the staffer is on administrative leave.

The penitentiary’s maximum security unit has been on lockdown since March 12. The unit holds about 560 prisoners, many serving life sentences for rape and murder.

Union president Danny Homan says Thursday the prison is understaffed and dangerous. Homan represents correctional officers in Iowa Council 61 of the American Federation of State, County and Municipal Employees.

Prison officials responded by saying they have worked to reduce the prison population and improve the ratio of guards to inmates.