A SOC analyst is monitoring network traffic and notices a large amount of data being transferred from the HR file server to an external IP address during off-hours. The server is supposed to be used only during business hours. The analyst checks the server logs and sees that a user account named 'backup_service' has been active and copying files. The 'backup_service' account is a service account that is normally used for automated backups, but the backup schedule is set to run at midnight, and the current time is 3 AM. The analyst suspects credential theft. Which of the following should the analyst do first?