Capturing Timestamp when Status Changes in a SharePoint 2010 List

I've created a Risk/Issue/Decsion Log (list) in SharePoint 2010.

I need to capture the date/timestamp when an item changes from 'Open' to 'Resolved' Status and also when the status changes from 'Resolved' to 'Closed'.

I'm using the default 'Created' field to capture when the item is created and the 'Open' status is selected. I've already created 2 more fields in the list to capture when the status changes from 'Open' to 'Resolved' Status and also when the status changes from 'Resolved' to 'Closed'. I just need help with how to automatically capture the date/timestamp in those fields.

I would greatly appreciate the help.

Thanks!