Several people in the management at the institution in Skänninge have received threatening letters addressed to them. Nine letters that arrived on August 13 contained cartridges, reports P4 Östergötland.
When there are different types of threats, there is often a thought behind it, often it's to scare into silence or influence in an improper way, says Elisabeth Anestad, regional manager at the Prison and Probation Service, to the radio.
The matter has been reported to the police and is being investigated as gross unlawful threats.
All those affected have wanted and been able to continue their work unhindered, according to the regional manager.